Photo Library is not the same as the camera roll. I don't use iCloud Photo Library. There should be a way to move those photos to a cloud based app like Box, Dropbox and OneDrive.
Using iCloud Photo Library will take your 5 free gb of iCloud storage space you need for back up. https://forums.imore.com/e?link=htt...mUvbUpU2480928%26subId2%3Dvbim&token=a8BZSEqK