To clarify, the album shows up as a whole album (like you popped the CD into a home hi-fi and listen to it from beginning to end), but when you sync it to your phone, it splits it up into multiple (or many) albums? I have this issue and at first was only happening to compilations, but now I noticed a single album with a single artist is now split into 19(!) different albums on my phone. I don't do subscription services and Apple Music is switched off.
What I noticed too...I'll import a compilation album (or any album now...smh) on the Mac. The first sync to the phone it shows up as 1 album! Then I'll import another album and I'll sync my phone. The previously synced album on the phone gets split, the gets further split with each sync effort. Also, it will show a different(!) artist completely unassociated with the compilation in question as the artist for that album in it's many instances.
Not really a solution, but to say you're not the only one...I made sure my various artists compilations were checked as compilations in MacOS Music, and since I started my new library, I have been diligent about filling in Album Artists and the sorting tabs for each albums too. It seems something is broken between the Mac/PC and the iPhone. This is is something Apple really needs to fix.
For the sake of experimentation, I am going to try to delete all the music on my phone and re-sync the 3,990 albums in my collection back over. It's going to take a day to do because I down-convert going to the phone so I can have everything with me. Maybe that's the issue? I will be reporting back on this issue because it has costed me a bit of sanity.
Cheers!
MacOS 15.5
iOS 18.5