One of problems found at the use of iOS 9 is iCloud backup that not working. Pop up or failure message that says “iCloud backup is failed” or “the last backup could not be completed” usually accompanying this problem. This problem is quite irritating since it disturb your comfortable use of iOS 9 performance.
To overcome this problem, it is important to make sure that your iCloud has enough space available and it has connection to a Wi-Fi and see whether the problem is still there.
Here are some potential solutions you can try to fix your problem. You can check the backed up data and how much the space needed by this process by taping the Settings, then tap iCloud, and choose Storage, then choose Manage Storage so you can set it up according to your preference whether you want to make some changes or not.
Try to reset your device by holding down together the Sleep/Wake and Home buttons for approximately 10 seconds until you see the Apple logo so that you can reset it directly.
Other option is by deleting the backup before turn it on again. You can follow these following steps to do that: after ensuring that you have backed up on iTunes in your computer, please tap the Settings, then tap iCloud, and choose Storage, then choose Manage Storage then please select your device and tap Delete Backup. The next, please tap the Settings, then tap iCloud, and choose Backup then please turn it off.
Restart your device, then go to Settings, then tap iCloud, and choose Backup then please turn it on, and then tap Back Up Now. If these steps are still not working you can try to reply this steps in other devices and access your iPhone back up data from that device. Those are some potential solutions that you can choose to overcome your iCloud problem.