Why isn't my phone doing an auto iCloud backup after iOS 8 update?

[iMore Question]

Auto iCloud backup not working after ios 8 update

I can manually backup, but I it won't do auto backups. My iPad will, but not my phone

 

[Just_Me_D]

Re: Auto iCloud backup not working after ios 8 update

The iPhone does an automatic iCloud backup, if enabled, "daily over Wi-Fi when your device is turned on, locked, and connected to a power source."

Source: iCloud: Back up your iOS device to iCloud

It does not say exactly "when".