It certainly doesn't make sense to trade Franco until/unless you know that Machado is coming, But all indications are they're done with him, and Santana/Crawford is our 3B tandem, and they will exceed his WAR easily. You replace the power/contact with your new OF. Because Hoskins at 1B and Santana at 3B > Santana at 1B and Franco at 3B.
Franco simply doesn't get you Renfroe, Phillies would have to throw in a prospect. He gets you a reliever or a back-up catcher or a bench OF.
Of course they might also trade Santana. It's not going to be an easy December for Klentak if Machado and Harper don't intend to sign until 2019.
(Edit: this blog rates Franco enough to suggest it would be for Stammens and a couple of prospects. I don't know about that, but nothing wrong with adding more depth because the Phillies are inevitably going to have to trade some of that themselves, whether this off-season or next deadline).