unable to delete or add songs to iPhone through iTunes

Dear All,

I'm using my previous iPhone (5s) as a music player - or trying to.

My difficulty is that, when I try to delete or add songs through iTunes, I can't. The 'delete' option is greyed out in the Edit menu, and - in short - any attempt to delete the songs 'On My Device' has no result. Using Manual Sync to add songs through drag-and-drop is equally ineffective.

Further: a large number of those songs On My Device are greyed out too, as if they're caught in mid-sync.

I have deleted all Music from the device itself, but it still shows up as above in iTunes.

I'm using iTunes 12.3.2, which I understand is the latest version. For the record, this is on a Mac Pro running Mavericks (10.9.5).

Any suggestions (Googling the question is not helpful) would be most appreciated.