I'm in agreement with everyone who says the bullpen is the biggest area of need. They could try Canterino out once he's healthy, but they need more than one new arm, and the trade route seems more likely to work out. Someone mentioned David Robertson as a possibility. Arizona also has a couple of guys that would be nice to have.
A starter would be another option. If the playoffs were to start today, the ALDS rotation would be Gray, Ryan, and either Archer or Smeltzer (personally I'd go with the lefty; there's also a good probability they'd use a four man rotation for the divisional round). The first two have the ability to keep them in the game with anyone, but that third spot would have me a little nervous. Montas is the obvious name, and he'd be solid. If the Phillies fall out of it, I'd love to see them make a run at Aaron Nola. Picking up a starter would allow them to move Archer and/or Smeltzer to the pen. I think the latter's stuff would play up. Archer probably is what he is, and I'd only use him if the game is already out of hand.