iCloud backup

When I start the backup of my iPhone to the iCloud, it gets stuck a little more than half way. I have tried the past three days to back it up and it starts out saying "1 minute" remaining, then it goes to "2 Hours" remaining, then to "3 hours" remaining and yesterday it went to "5 hours" remaining. I have had it connected to WiFi, plugged in and backing up since 6:15 a.m. and it is now 11:29 a.m.

What is the problem?