Players have value to the Phillies, Hellickson had value until he fell below replacement level. He was a competent innings eater last year and this April.
Galvis has significant value, especially if they've turned the corner and are becoming competitive.
It doesn't mean you don't trade him, however, it does mean you have a real threshold of value before you'd consider trading him, that is, he has enough value to the team (especially the young starting pitchers) that you want something in a trade sufficient to compensate for that lost value. You'd rather obtain that value (maybe through next July) and trade him for less than just trade him for a limited package. If current offers or December offers aren't that good, he has more value to the Phillies, and any decline in value is meaningless.
There's a knee jerk willingness to trade everyone over the age of 25 that's a bit bewildering, In July 2015 we started the rebuild, at that time you're dumping assets for prospects, next year we're in year 3, we've collected plenty of assets, sure, more is better than less, but at some point you have to start fielding a competitive team or both the fans and players give up. So as the team improves, there's less need to garner assets and more need to field a solid team (not "win now mode, but "win soon" mode).
There's just no urgency right now, this team is becoming competitive, I see no reason for "one step back, two steps forward" moves.
There will be plenty of opportunities to move people over the next year to two years as prospects show they're ready, but why not wait for Kingery to have a long enough track record to be confident he can step in before you trade Hernandez? This is not a Clff Lee/Hamels situation, move them a year early when they have a lot of value rather than a year late when they may have no value - no one currently proposed as trade bait has that kind of value.