Phillies are also pushing young pitchers to rely on their secondary pitches.
Used to be that sliders were blamed for arm issues, but I think it's becoming understood that the pressure for velo has too many pitchers overthrowing which puts more stress on their arms.
If you're throwing more changeups and sliders, you don't have to throw as many FBs, or throw them as fast, when hitters are seeing a steady diet of off speed stuff, a 95 FB looks as fast as 98 because they can't just sit on it.