how to delete music listed "on my device" in the apple device app PC

so i'm having a **** of a time trying to sync my imported music from my PC to my iPhone15, all software is up to date. sometimes it syncs some, sometimes most just never all my music.

its as though it thinks the music is already on my phone and skips it.

if i delete all my my music files in the iphone storage menu to start fresh - my entire collection is still listed in the "on my device" section in the Apple Devices app. is there a way to clear/delete this content?

thanks!!