There are 16 steps shown in this sutta.
"Now how is mindfulness of in-&-out breathing developed & pursued so
as to be of great fruit, of great benefit?
"There is the case where a monk, having gone to the wilderness, to the
shade of a tree, or to an empty building, sits down folding his legs
crosswise, holding his body erect, and setting mindfulness to the
fore.1 Always mindful, he breathes in; mindful he breathes out.
"1 Breathing in long, he discerns, 'I am breathing in long'; or
breathing out long, he discerns, 'I am breathing out long.' [2] Or
breathing in short, he discerns, 'I am breathing in short'; or
breathing out short, he discerns, 'I am breathing out short.' [3] He
trains himself, 'I will breathe in sensitive to the entire body.'[2]
He trains himself, 'I will breathe out sensitive to the entire body.'
[4] He trains himself, 'I will breathe in calming bodily
fabrication.'[3] He trains himself, 'I will breathe out calming bodily
fabrication.'
"[5] He trains himself, 'I will breathe in sensitive to rapture.' He
trains himself, 'I will breathe out sensitive to rapture.' [6] He
trains himself, 'I will breathe in sensitive to pleasure.' He trains
himself, 'I will breathe out sensitive to pleasure.' [7] He trains
himself, 'I will breathe in sensitive to mental fabrication.'[4] He
trains himself, 'I will breathe out sensitive to mental fabrication.'
[8] He trains himself, 'I will breathe in calming mental fabrication.'
He trains himself, 'I will breathe out calming mental fabrication.'
"[9] He trains himself, 'I will breathe in sensitive to the mind.' He
trains himself, 'I will breathe out sensitive to the mind.' [10] He
trains himself, 'I will breathe in satisfying the mind.' He trains
himself, 'I will breathe out satisfying the mind.' [11] He trains
himself, 'I will breathe in steadying the mind.' He trains himself, 'I
will breathe out steadying the mind.' [12] He trains himself, 'I will
breathe in releasing the mind.' He trains himself, 'I will breathe out
releasing the mind.'[5]
"[13] He trains himself, 'I will breathe in focusing on inconstancy.'
He trains himself, 'I will breathe out focusing on inconstancy.' [14]
He trains himself, 'I will breathe in focusing on dispassion
[literally, fading].' He trains himself, 'I will breathe out focusing
on dispassion.' [15] He trains himself, 'I will breathe in focusing on
cessation.' He trains himself, 'I will breathe out focusing on
cessation.' [16] He trains himself, 'I will breathe in focusing on
relinquishment.' He trains himself, 'I will breathe out focusing on
relinquishment.'
"This is how mindfulness of in-&-out breathing is developed & pursued
so as to be of great fruit, of great benefit.