Backing up your iPhone is always a good idea. Your phone may be behaving badly and you hope that you can fix this by resetting it to factory default and applying the latest backup. Or you are upgrading to a new iPhone and want to transfer all your current data. Regardless of the reason, you can back up your phone and restore the backup to iPhone and iPad or iPod touch as needed.
Apple offers some backup methods. Windows users can back up their phone through iTunes. Users of macOS Catalina can use the Finder. You can also secure your phone in iCloud.