Kepler was a FA anyway and was not good last year.
The Phillies have two options if they sign Bichette:
Bichette, Turner, Stott trade off between 2B, 3B and SS and the Phillies trade Bohm for a catcher.
or
Bichette takes over SS and Turner goes into LF, with Adolis Garcia in RF and Marsh/Justin Crawford getting CF.
The Phillies may need to trade Bohm anyway and they are not going into next year with Marchan/Stubbs as the catchers. It's also no secret Castellanos has played his last game with them. I'm sure they're trying to trade him before outright releasing him. I could see the Reds interested in brining him back since their OF is bleak.