iTunes shows songs on phone but phone doesn’t

Hi! So my dad has an iPhone XR with the latest iOS. He uses iTunes on a Windows 10 PC for backups and adding music. Last week he deleted all musing from the phone in order to ’reorganize’ his playlists. When he went to add the music and playlists back to his phone, the phone shows having songs and playlists already on it when clicking on it in the tree in the left hand side of the iTunes window. However his phone doesn’t show any songs or playlists when going to the music app. Furthermore there is no space taken up by music when looking at the bar chart. Synching the phone just goes through a back up and ‘changes’ but no music is being transferred.

Any ideas?