Follow the steps below to verify your iPhone is completing a backup.
1. Go to Settings on your iPhone
2. Click on your Name
3. Click on iCloud
4. Verify iCloud Backup is "On". Click Verify iCloud Backup to manually create a back up or see your most recent completed back up.
5. Click Backup Now to manually create a back up
6. This is where you can see when your last back up was completed