John is frustrated that he can't delete the pictures on his phone without deleting them from iCloud. Leo says that if he selects "optimize phone storage" in settings, it will delete it on the phone without deleting it on iCloud. But he'll have to select "Keep Originals" on his Mac so it doesn't delete there.
A better option is to use Google Photos. It's free and it will back up everything on the phone. Then he can select "delete everything I've backed up" and it will remove the photos from the phone, but keep them in the cloud.