I have a different version of this problem. I use iCloud to sync photos between 2 phones, a MacBook and a Windows desktop. Recently I've been transferring via a cable connection astronomy photos taken by the NightCap app to my desktop for stacking & editing. Twice in the past month a LOT of photos including some from before I had an iPhone have appeared on the phone. This fills up my iCloud storage and it is a pain to delete them. I'm guessing the problem is related to transferring photos from the phone to the desktop. How do I prevent the reverse transfer to the phone?