What are the differences of Phala Samapatti between each stage of sainthood? The fruit of each stage of Sainthood possibly would be different. Hence there would be some distinction and differences between the stages of sainthood.
The fruition consciousnesses are classified as being resultant consciousnesses (vipākacittāni) so they differ based on what the wholesome consciousness produce them, so the difference between the fruit of a stream-enterer and a sakadagamin is the wholesome consciousness that causes them. For the fruit of stream entry, the wholesome consciousness that causes it is the path consciousness of stream entry, and for a sakadagamin it is the path consciousness of a sakadagamin.
Then one will wonder what is the difference between the different path consciousnesses. That is an easier question to answer. It is the path consciousnesses that cut through the fetters. The path consciousness of stream entry cuts through the first three fetters, the path consciousness of a sakadagamin weakens desire and ill-will, etc...
For more information on this I would recommend reading §26 and §27 of A Comprehensive Manual of Abhidhamma and chapter 22 of the Visuddhimagga. Both of these books are freely and legally available online as PDFs.
This describes different stages of Phala Samapatti
Here is the Phala Samapatti progessions http://www.palikanon.com/english/practice_insight/characteristics_of_forgetting.htm