I understand your iPhone is not completing the iCloud backup due to storage issues. I'd be happy to help.
I suggest using the article and information below to get backed up:
If iCloud Backup couldn’t be completed or you can’t restore - Apple Support
Cheers!If an alert says that there's not enough iCloud storage
This message appears when you need more iCloud storage to back up (The available space on your iOS device is different than your available space in iCloud).
Here are some things you can do:
- Upgrade your iCloud storage plan.
- Make a smaller backup. You can back up fewer apps or delete unwanted photos and videos.
- Delete older backups that you don't need.