iPhone 5 backup to iCloud not starting I have tried to start my back up manually because the automatic back up isn't working for some reason. The last backup was June 3, 2015. I have the icloud backup on and I have plenty of space in my icloud!
In- order to Fix the Automatic iCloud Backup not Working issue on iPhone do the following steps ;

Step:1

Delete your iCloud profile in iPhone

Step:2

Now again reconnect the icloud profile

Step:3

Now you get message sync automatically..

Well also , check this below article to troubleshoot this issue ;

https://support.apple.com/en-in/HT203271

Hope this helps...