My iPhone won't back up at all I have just upgraded my phone and I need to ensure everything transfers accurately. However my iPhone is not allowing me to back up. Not on iTunes or iCloud. 

I have tried plugging it into my mac to backup and nothing happens. The last back up was last week, and I know its petty but I want to transfer everything over, not a week old transfer. 

When I go to System Preferences > iCloud > Backup - I press "Backup now" and it says estimating time remaining and then "The last backup could not be completed."

I am connected to a strong Wi-Fi. I have storage on my phone but it's still not working.
I've had it where i can't back up my iPhone and it's to do with 'sharing' in the iCloud settings. Go to iCloud in System preferences and it should guide you from there.