Delete some music from iPhone, keep all of it in iTunes on Win10 laptop
Context: All my music is in iTunes on my Win10 laptop. Almost (not quite all) of that is music I ripped from CDs that we own, i.e. only a small portion is downloaded from iTunes Store. I sync some of that music from laptop to my iPhone 6s: the iPhone holds a subset of the laptop iTunes library. I'm trying to reduce what's on the iPhone w/out losing it fr the laptop library. And last time I tried it was a disaster, trying to do it right this time.
The problem: I searched for "delete music from my iPhone," and the instructions said to use Apple Music on iPhone and delete. However, the last time I deleted music directly from my iPhone 6s, the next time I synced to iTunes, it butchered my library, took me hours to get it back from a reasonably recent backup, figure out the changes, etc. A serious pain, I want to avoid doing that again. That was a year or so ago, now I'm running outta space on iPhone.
What I want: I need to delete a bunch of music from my iPhone 6s (iOS 13.2, latest iTunes update installed). I don't want to lose that music in iTune on my laptop (Win10, system is also fully updated), nor corrupt my library. Just wanna delete some of my music from my iPhone.
What's the recommended process? Thanks for your guidance, and please excuse my obvious worry, this was a total horrorshow last time.
Alex
Windows, Windows 10