not syncing photos on new phone

A relative of mine just got a new iPhone 15, upgraded from the XR. She had the cell provider transfer everything on her new phone.

Since then, it’s been glitching and freezing because it’s still syncing all her photos to iCloud, but saying her iPhone storage is full (this has been 2 days now). She has a crazy amount of photo, 37,000, but only 1700 are in iCloud. She has deleted a lot of unused apps, but the phone won’t let her delete photos or videos on her phone. Now she’s having a hard time even receiving messages