Songs duplicated on iPhone after I synch with IMac

I have a very old music library that I have maintained over the years with apple products. I have the issue that when I synch with my IMac, all the older songs (1700 out of 1800) are now on my iPhone twice. I’m thinking the easiest way to fix this is to delete all the songs off of my phone and resynch with my IMac. I’m afraid when I delete all the songs of my phone though it might automatically delete them out of the IMac’s library as well. Any advice how to clean this mess up would be greatly appreciated. iPhone 13 Pro and a late 2015 IMac.