phyto doesn't hurt but isn't necessary.
from what your saying it sounds like you have the clam between two rocks? this may prevent the clam from opening. if he hasn't planted his foot, it usually means he isn't happy with his location. has he been trying to move?
bury a small flat rock ( oyster shell, clam shell ..... ) just below the surface of your sand. then place the clam on top of the rock and use some sand to prop him up. sometimes they attach right away ( a day or so ), other times it takes a week or more.