Rather than make my own thread...
I've turned on manual management of music and videos and synced my iPhone - without actually selecting any music to sync.
iTunes says I've got 25GB free on my iPhone with only a few songs, but my iPhone says I've only got 2.2GB. It hasn't actually deleted any music and I can play it still.
I've tried turning off 'show all music' and this makes no difference.
When I go to settings > general > usage it shows "No data" under music, but when I go into the music app all of my songs are still in there... not just the ones I've purchased in iTunes, but every track I synced to the device.
iTunes thinks I have no music on there and the phone doesn't seem sure, because my overall free space is low but it thinks I have no data in music. So it seems conflicted about what's going on.
Any ideas about how I can delete music? I have thousands of songs on there so I'm not going to swipe to delete it all...
I'd rather not restore if I can help it, but that will be my next step if no other suggestions.
Thanks