After you back up your iPhone or iPad, you have a copy of your information to use in case your device is ever replaced, lost, or damaged. You can back up your device manually, or turn on iCloud Backup to automatically keep your device backed up.
Tap Back Up Now. Stay connected to your Wi-Fi network until the process ends. Under Back Up Now, the date and time of your last backup is shown. If you get an alert that you don't have enough iCloud storage space to complete the backup, follow the onscreen steps to buy more iCloud storage.
Automatically back up with iCloud Backup
Go to Settings > [your name] > iCloud > iCloud Backup and make sure that Back Up This [Device] is turned on.