In this video by Sayadaw U Nandasiri, if I am understanding him correctly, he equates appana samadhi and magga/phala enlightenment. Is this correct? I had understood momentary, access, and absorption to be referring to jhana. Do they also refer to magga/phala? Or are they one in the same?
I cannot answer the first part of the question so i will instead address the other part of the question, i.e.
"I had understood momentary, access, and absorption to be referring to jhana".
The following quote on the 3 different types of concentration is from the book "Practicing The Jhanas" by Tina Rasmussen and Stephen Snyder. They were both students of Pa Auk Sayadaw and undertook a Samatha Meditation Course under his guidance. They write in the book that they achieved the 4 material jhanas and the 4 immaterial jhanas. Here is their description of the different types of concentration and in what practices they appear:
Momentary concentration is the most difficult to understand, because there are two types. The first develops in vipassanā practices in which the object changes frequently. In contrast to samantha practices in which the object is constant, in vipassanā the object is, in a way, changing or “moving.” As such, one could say that the ultimate object of vipassanā meditation is the present moment and what is being perceived in the present moment (hence, the relationship to “momentary” concentration).
Insight-oriented momentary concentration practices are widely used and can be found in meditation such as vipassanā (as it is commonly practiced in North America and Europe) as well as in the Tibetan dzogchen rigpa practice and the Zen shikantaza practice. The Venerable Pa Auk Sayadaw presents the four elements meditation, which is a momentary concentration practice, as the entry point into the vipassanā practices. We describe this practice in chapter 8. The second type of momentary concentration arises during samatha practice.
The Venerable Pa Auk Sayadaw sometimes refers to this type of momentary concentration as “preparatory” concentration, because it prepares the meditator for and precedes access concentration (the second type of concentration). In samatha practice, the meditation object is consistent rather than changing. Having a consistent object leads to serenity and purification of mind.
Meditators can eventually attain access concentration using either type of momentary concentration practice—samatha or vipassanā. However, samatha practices are more likely to lead to access concentration because of their more stable nature. Access concentration is characterized by the significant reduction or complete dropping of the five hindrances and the arising and strengthening of the jhāna factors. For most people, a period of intensive practice is required to reach access concentration. In access concentration, the meditative experience becomes smoother, easier, and more pleasant because of this lessening of hindrances and the arising of the powerful and blissful sensations of the jhāna factors. This allows meditators to meditate longer and progress more easily in the practice.
It becomes a positive, self-reinforcing loop.It is easy to confuse momentary concentration with access concentration. One difference is that with access concentration, the meditator’s continuity with the object is much longer and more stable over time. Another difference is that with access concentration, the object is much more energized and “bright.”Most of the practices outlined in this book are samatha practices specifically designed to settle the mind and develop laserlike awareness, leading eventually to full absorption into the jhānas. Examples of samatha practices designed to develop access and absorption concentration are ānāpānasati meditation (as presented by the Venerable Pa Auk Sayadaw), the kasiṇas, thirty-two-body-parts meditation, skeleton meditation, and the bramavihāras (sublime abidings).
As access concentration develops, but prior to full absorption, it is also easy to confuse access with absorption concentration. In access concentration, the jhāna factors are present but insufficiently strong for full absorption into jhāna. (The differences between access and absorption are described below.)Even after a meditator has experienced full jhāna absorption and begins to move through the practice progression, access concentration continues to be used. With progression to each successive jhāna, the meditator first experiences access concentration as the awareness orients to the new experiences and increases in stability.
The words jhāna and absorption are synonymous. In absorption concentration, awareness is pulled into the jhāna with a “snap.” The beginning meditator cannot “will” the absorption to happen or “make” it happen. Full absorption arises only when the concentration is strong and ripe after many days, weeks, months, or even years of unwavering focus on a specific meditative object. Only later, as a meditator becomes more experienced with full jhāna absorption and more skilled with the progression of jhānas and the five “jhāna masteries,” is it possible to enter a jhāna at will.
The five jhāna masteries are specific attainments that meditators complete in each jhāna, as demonstrations of mastery, before they can progress to the next jhāna. They are described in chapter 5.In absorption, in addition to the strong presence of the appropriate jhāna factors, the awareness is extremely secluded and focused, and ongoing concentration is more easily maintained. Awareness fully penetrates and is suffused by the jhāna factors. The Visuddhimagga highlights the difference between access and absorption concentration using the analogy of walking. Access concentration is like a toddler learning to walk. The child can take a few steps but repeatedly falls down. In contrast, absorption concentration is like an adult who is able to stand and walk for an entire day without falling down.
A modern metaphor would be of a top spinning. In access concentration, the top needs constant attention, wobbles frequently, and falls down. In absorption, the top spins in a centered way on its own.There may be misconceptions about the experience of full absorption in jhāna. First, there is awareness while in jhāna. It is not a zombie state, trance, or period of unconsciousness. However, there is no sense of “me” while in jhāna. The only awareness while in full absorption is of the object. If meditators have awareness of data from the five senses, it is because they are temporarily out of absorption. The five senses (sight, hearing, touch, taste, and smell) do not arise while in absorption jhāna. In addition, there is no thought or decision making while fully absorbed in jhāna.
Beginning meditators who find that they are thinking or noticing input from the sense doors should view this as a slight imperfection of jhāna rather than full jhāna absorption. Meditators can also “pop out” of jhāna unintentionally because concentration wanes and the jhāna factors lessen. It is best not to worry about initial imperfections, which are bound to happen as beginners are developing mastery of the jhānas. As concentration increases, these imperfections wane and stability increases.Awareness in the jhānas is incredibly pristine, purifying, and indescribable. It is distinctly different from access concentration. Because access concentration can be so pleasant and nonordinary, however, people sometimes mistake access concentration for absorption, when it is not. This is one reason why it is important to receive guidance from a qualified teacher who knows the difference between access concentration and absorption concentration.
Absorption concentration is an incredibly powerful tool for purification, refinement of awareness, and access to realms far beyond normal, everyday comprehension. In addition, this intense focus can be an incredibly powerful tool to apply to the vipassanā practice. Meditation powered by the supercharged energy of the jhānas, or even a strong access concentration, can provide a vehicle to insight beyond normal perception that may not be possible with momentary concentration alone.We should note that, because awareness is so refined in full absorption, sensory input that would seem minimal in ordinary consciousness can feel extremely jarring when emerging from jhāna. This experience is intensified further when a meditator has completed weeks or months of deep absorption practice and reenters worldly life.
What the venerable means is that, according to the abhidhamma, magga and phala are both types of appana samadhi, not that all appana samadhi is magga and phala (which would be silly anyway, because magga and phala themselves are distinct from each other). At the moment of enlightenment, one enters into a type of appana samadhi called "lokuttara samadhi", or "lokuttara jhāna" (lokuttara meaning supramundane).
katame dhammā kusalā? yasmiṃ samaye lokuttaraṃ jhānaṃ bhāveti niyyānikaṃ apacayagāmiṃ diṭṭhigatānaṃ pahānāya paṭhamāya bhūmiyā pattiyā vivicceva kāmehi . pe . paṭhamaṃ jhānaṃ upasampajja viharati
What dhammas are wholesome? At whatever time, one cultivates supermundane jhāna that leads out (from samsara), that goes to diminution (of suffering), through the abandoning of gone-to views, through attaining the first realm (stream entry), having become thoroughly secluded from sensuality ... one enters and abides in the first jhāna.
-- DhS 277
As a non-English native, it may be that he is not aware of the potential ambiguity of his grammatical structuring of the statement.