This is exactly why I switched to Google Photos. They let you back everything up to the cloud and then delete on your device to make space. The way Apple handles cloud storage makes so little sense that it took me a while to understand. Wish I had never tried Apple cloud. All it did was create big blank patches in my photos and now won't play my videos. Between trying it out and switching back I know I've lost some things. At least from here on out I won't have to worry.