Like the title says I think phoenix down is currently little more than a courtesy rez for our fellows in the field. It has so much wasted potential! Imagine your any non healer class that isn't a summoner. you can now rez your healer just in time! Or maybe help your healer out by rezing that blm or dragoon that keeps dying.
Considering it can't stack and it has a long cast time I don't feel this is op at all. It would be one use per dungeon and a great help. Instead of being that item you use to rez your best friend who just started.