I think it's just a shame that the Mitchell unit has completely disappeared. No Ronnie, Grant, Sam, Peggy, Ben etc. Shirley wants nothing to do with him, Jay has moved on...
I'd actually like to see his daughter Louise return but the only way that could happen would be if Lisa died off screen but that'd be too coincidental to the whole Kathy/Ben situation. Maybe in a few years when Louise is 16 years old, she can come and find Phil and then gradually, they could build up a strong bond and Phil finally does something right with his own family. Other than that, what is left for Phil?
Maybe when Roxy and Alfie inevitably split up, maybe she moves in with Phil?