Restore backup on phone device

If you have had Settings>[name]>iCloud>iCloud Backup turned on, then you can use that backup to restore you phone back to where it was at the time of the backup. “Restore” is what you do when you buy a new phone, so this safety, if you have it set, requires you to erase everything on your phone and replace it with the backup.

You can see this:

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support