Don't do that. I would use cloud based apps like Box, Dropbox and OneDrive. Upload photos to those apps, then delete the photos from your camera roll. You can set up photo folders and subfolders to organize your photos. Videos too. You could use iCloud Photo Library, but it uses up your iCloud storage space you need for back up. Box offers 10 free gb of storage. OneDrive offers 30 free gb of storage. Why are you needing to free space? What else do you have on your phone that's taking space? Music? Messages?
Sent from my ancient but trustworthy iPhone 5.