allentown - If we take as a given your positive view of Galvis - that his 2018 will be similar, or better than his 2017... what do you want the Phillies to do with him? Options:
1) Trade him this winter.
2) Hang on to him for now, trade him in July/August.
3) Hang on to him for 2018, let him leave as a FA next winter.
4) Extend him.
Under any of the last three options above, there are additional issues to be decided. Where does Galvis play? Who gets the playing time, among Hernandez, Galvis, Crawford, Franco? Are you advocating that we give up on Franco now? Or that we trade Hernandez and move Galvis to 2B? Or that we limit Crawford's playing time? Or that we have some kind of "four guys for three positions" daily changes in the lineup - recognizing that Hernandez and Crawford have a particular offensive profile (high OBP, top-of-the-order hitters) that Franco and Galvis do not? Are we going to go into half of our games with a guy with an OBP of around .300 in the top of the order, when we have two table-setters who are likely to be posting .350 or better OBP?
Now, if you want to give up on Franco, and put Galvis in the eight-hole as your everyday 3B next April...I could see that, recognizing that Galvis' tenure there is short-term (given the impending FA, and probable trade mid-season) - and assuming 1) Hernandez can move to 3B effectively, and 2) Kingery can come up mid-season and produce similar overall value as Galvis. This would be a "trade Franco now, trade Galvis later" approach. The trade returns probably wouldn't be very exciting - this is more "addition by subtraction" in the case of Franco, and trading off an impending free agent in the case of Galvis.
If your goal is trade value, then Cesar Hernandez is the guy with value - three years of team control, OBP of .370 over the past two seasons, 27 years old. OTOH, if they think Hernandez can handle 3B, one might argue that they'd be crazy to trade him, regardless of what they think Kingery can be. In today's game, .370 OBP players don't grow on trees.