Photo Synchronization to iCloud Not Working - Back-up Will Not Resume.

Dear Community,

My wife’s iPad and laptop have no problem synchronizing new photos to iCloud. But her iPhone will not synchronize any new photos taken. It continues to say out of memory in iCloud despite my plan being upgraded and plenty of space available.

I have tried turning off iCloud and restarting it, and that worked at first, then the problems started again. In the photos app, it states that the photos cannot be backed up and no option to resume.

Does anyone have any thoughts?