Cannot Unsync Photos from iPhone

[PixelDestructor]

I’m having a strange problem and I’m hoping someone on here can help me. In the past, I would sync all of my photos from my Mac to my iPhone. However, I have since wanted to remove all of the photos that I synced from my Mac and leave only the photos in my iPhone’s Camera Roll, but I am unable to do that. I’ll go into iTunes, uncheck syncing with the Photos app, and let my phone sync, but no photos are removed. I still have all the photos from my Mac and the Faces from my Mac as well. How can I get rid of these for good? They are taking up a lot of space on my phone and I don’t want them anymore