Q: Iphone 5 - Can't back up

Hello there, Karen.

Some users with issues similar to your's have found that performing a Restart or a Force Restart and then trying to make the iCloud backup has resolved it. The following Knowledge Base article offers the steps on how to perform a Restart/Force Restart:

Restart your iPhone, iPad, or iPod touch - Apple Support

Once you've done that, then use the following information to perform the backup once more:

How to back up your devices using iCloud or iTunes - Apple Support

Make a backup using iCloud

1. Connect your device to a Wi-Fi network.
2. In iOS 8 or later, tap Settings > iCloud > Backup.
   In iOS 7 or earlier, tap Settings > iCloud > Storage & Backup.
3. Make sure that iCloud Backup is turned on.
   
4. Tap Back Up Now. Stay connected to your Wi-Fi network until the process completes.
5. Make sure the backup finished by tapping Settings > iCloud > Storage > Manage Storage, and then select your device. The backup you just made should appear in the details with the time and backup size.

Follow more steps if you need help making a backup in iCloud.

 

If the issue persists, then repeat with the Force Restart steps.

Thanks for being a part of Apple Support Communities.

Cheers,

Pedro.