Our trainer said to use whatever word/phrase you feel comfortable saying as long as you stay consistent. We use the Poochie Bells and always use the same phrase (outside potty, ring the bell) but now that she has the bells down to a science we just say outside potty. Once outside - I use, "Izzy go pee-pee and then Izzy - go poopie - also the phrase "hurry up" so she doesn't dawdle - well - she still does but not as much when I tell her that.
Cause that girl is always on squirrel/mouse patrol!!