Phone won't turn completely off or completely on.

6s Plus iphone will not turn completely off or completely on. Just get apple on screen. Had been getting messages phone was almost full...and iCloud was also full so it wasn't backing up. I purchased additional icloud storage. Plugged phone into computer (which I never do) and phone didn't show up in itunes. Really don't want to hear phone has to be erased... Please help. Thanks