How do I delete my entire music library from the "on this iPhone" tab in itunes?

I just bought a new mac book and my itunes library is empty (which is how I want it to be for now). When I plug my phone in under the "on this iphone" tab there is a whole music library that I would really like to get rid of (since the "!" keeps coming up because the files are not actually on my new mac). I have already deleted all the music from my iphone by going to setting>usage and swiping "music" to delete but its really annoying that the songs still come up on the music library under the "on this iphone" tab when I plug in the phone. I have tried everything but nothing seems to work. Can anyone help me?!?!?!