What is an option called photo library on iCloud back up?
If I turn off photo library in back up and turn on iCloud photo to sync in iCloud, are photos on my phone stored in iCloud?
If you sync with iCloud, your photos will no longer be in your device backup but rather sync to iCloud. You can also elect to optimize so that lower resolution images remain on your device with originals in iCloud. Otherwise, all files remain on device at original resolution. If you delete a file on device, it deletes everywhere