Can't Backup iPhone 12 Pro Max to iCloud

I have an iPhone 12 Pro Max that I'm trying to back up to iCloud. I have about 13g I want to back up. I have 50g of iCloud storage. When I try to back up, it starts and just sits where it is without the blue line moving and with the little grey "star" moving. I've signed out and signed back in to iCloud. When that didn't work I reset all my settings and tried again. The same thing happens. I can back it up to iCloud on my MBP but not on my iPhone. I've deleted all previous old backups of my previous phone, but nothing seems to help. I have it plugged in while trying. I also tried last night, locked screen and plugged in. What else can I try? I have a full backup on my MBP, but I really don't want to do a complete start over, as I have an app that keeps track of my daily progress on something and I would lose over two years of tracking on it. Any suggestions would be appreciated. Thank you for help that you can provide.