Q: Iphone message says last backup could not be completed

If other suggestions found in the forum don't help in this matter, then...

Backup not successful:  I had the same problem.

My solution was to turn off some apps (Settings>iCloud>Storage & Backup>manage Storage, tap my device name in the Backups section, then look under Backup options) and try a manual backup.  If it didn't work, turn off a few more apps and try a backup.  Keep doing that until the backup works.  Then try adding in some of the last batch of apps that were previously turned off - the objective is to find the app that causes the backup to fail.  For me, I suspect that the one app I found had a bad data file that, when included in the backup, caused the backup to quit.

This can be a long process if you have a lot of apps that you originally turned on for backups.

What works fine for me was to delete the whole backup of the device and restart it.

Working fine now.

I turned off all apps - everything - deleted backup and restarted.  Nothing works. Phone will back up to computer no problem but will not back up to ICloud.  Just sits there forever saying "Backing Up... Estimated time remaining..." , blue bar never moves.  Finally times out and says "Last Back Up..Never, Back Up Incomplete". (Yes it is plugged in and locked).  My boss expects me to have this done by tomorrow - any ideas???