One way, I suppose, to improve the bullpen (albeit with two many lefties) is to put Ranger there and then add a starter. There's always the option of managing Ranger's innings so he can be restored to the rotation come playoff time, hopefully at better strength than he's been showing lately as the season slogs along.
A move to acquire a starter also allows the luxury for a team with an 8-game lead to move to a six man rotation, conserving everyone's strength for the playofffs.
The big play, I guess, would be to trade for Crochet and immediately move to a six man rotation. The worry with Crochet is that he'll be spent when the playoffs arrive, and the Phillies have the big advantage here in being in a position to conserve his innings,