Basically what the subject states. Does phase step qualify as casting dimension door for the purposes of the dimensional agility chain?
Phase step:
You instantly transfer the touched creature to a point you designate within range. This otherwise functions as the spell dimension door, except that you must have line of sight and line of effect to the target’s destination for this spell’s effects to properly function.
Dimensional agility:
After using abundant step or casting dimension door, you can take any actions you still have remaining on your turn. You also gain a +4 bonus on Concentration checks when casting teleportation spells.
No. Phase Step is a lower level variation of dimension door, it is not dimension door nor is it considered to be dimension door. The line “ This otherwise functions as the spell dimension door” just means to refer to dimension door for the spells rules and make the changes noted in phase step. Note: it is specifically weaker, and every class that can get Phase Step also gets Dimension Door (except alchemist).