Was attempting iCloud backup from iPhone 6+ and tried to "cancel backup" now the wheels are spinning and the screen is frozen. How do I make it stop??

Was attempting an iCloud backup initiated from my iPhone 6s+. Needed to leave before it finished, so I tapped on "Cancel Backup" That didn't seem to work. Six hours later the wheels are still spinning around. Screen message says "Turning on Backup" -- it is also spinning around and the screen seems to be frozen as I cannot get back to Setting after I selected "iCloud" How do I fix this?