Your “non-Apple Music” playlists/music files shouldn’t be affected tho. (After Apple Music sub. ends) Am not an Apple Music subscriber since I had it briefly for 3 months as a promo with a new Apple device, but it didn’t affect my old existing playlists/ripped music files in my “ iTunes” (iTunes has been gone for Mac users for awhile...now the Mac music App is just called “Music” (not to be confused with the “Apple Music subscription”)...the program is still called “iTunes” on Windows I guess.
Looking at your response, you seem to have access to your music on your iPhone without maintaining the subscription to Apple Music service. I will be attempting your suggestions on my sons phone shortly, next time I have 3 weeks to commit to simple file transfer.