Cloud Backup is a service from Apple which backs up the entire contents of your device to the cloud. If the device is lost or broken, you can set up a new phone and restore the backup, so your new phone has all the apps and files your old phone had. This is the best way to be sure you do not lose your Locker files, which would otherwise be deleted if app was deleted, or device is lost or broken.
How to check if iCloud backup is enabled:
1. Open your iPhone settings and tap on your Name / Apple ID, then choose "iCloud"
2. Look for iCloud Backup and make sure it is set to "On":
3. Next, confirm that Locker files are stored in your iCloud backup by tapping "Manage Storage" > Backups > Your Device > Show All Apps > Locker and seeing that the toggle is "On" and file size approximately matches the total size of your Locker files.