I agree with having Smith taking some of the load off Sam's shoulders for this game - you never know, it could be the game he shows what he can do....
The big worry with that is what you gain in experience (ish) you lose in defence when Smith's on, and against Saints that could be a nightmare.
Also agree that Tommy's probably been our best hooker this year, but he's also been one of our best players full stop - so I wouldn't waste that by having him on the bench for any part of the game.
As for Phelps at half back, afraid you're on your own there