Removing the iCloud back up message I've been getting messages of the form

iPhone Not Backed Up
This iPhone hasn't been backed up in 141 weeks. Backups happen when this iPhone is plugged in, locked and connected to Wi-Fi.

I have the basic, free 5GB iCloud plan. I've turned off the storage for many apps, including Photos. Making my iCloud use only 594MB.
Is there a way to make it stop?
You can disable iCloud Backup in Settings → Apple ID → iCloud → iCloud Backup by switching the switch off.