iPhone is not backing up to iCloud
The reason behind is because your device is not locked.
As stated in this Apple document that in order to "Automatically back up with iCloud Backup" 


Make sure that iCloud Backup is turned on in Settings > iCloud > Backup
Connect your device to a power source
Connect your device to a Wi-Fi network
Make sure that your device's screen is locked
Check that you have enough available space in iCloud for the backup