so, somehow prue can kinda, make a "ghost" physical version of herself, while her real version is safe? if you get me? so, she can be in say her bedroom and then imagine herself to be in the kitchen? according to the charmed wikia:
Astral Projection is the ability to project one's consciousness into an astral form outside the body. When a person astral projects, their physical body falls to the floor, slumps over or remains still until they return.While in "astral mode", powers are dormant. However, some advanced users have mastered the skill to use their powers whilst astral projecting.
and i think phoebe's powers were more passive (unlike you know blowing things up and moving things) so they aren't as noticeable! also, the amount of times they change (i.e. her becoming the wife of The Source and having evil powers, and then the flashbacks to when she was evil in another life) is so confusing!
that said, i haven't read the comics so i'm not sure if they change in that or not!