How do I know what files on my iPhone have been backed up if it isn't working?

I may be in the position where restoring my iPhone is my only option. I'm aware this wipes all data but I don't know what has been backed up and what hasn't. Is there a way of discovering what files have been backed up on my iCloud? I have tried accessing this through iCloud drive via my iPad (which is on the same iCloud account) but it says that there are 0 items in it yet the majority of my iCloud storage has been used up. How else am I to find out what has been backed up on my iPhone?