The device must be connected to a Wi-Fi network to save a back up to iCloud.
From the home screen, tap Settings.
Scroll to and tap iCloud.
Scroll to and tap Storage & Backup.
Ensure that iCloud Backup is enabled, then tap Back Up Now.
Wait until iCloud finish backing up the iPhone. It may take up to 30 minutes for the device to finish.
The iPhone is now backed up using iCloud.