Can I Delete A Photo On My Iphohne 6 But Still Keep It On My iCloud? Here's The Answer.
The photos have to be saved to one device in order to stay in the cloud. A good place is to save them to the PC or Mac and share them from the cloud there.
Here’s the tricky part. If you delete a photo, it will delete it from all devices. The way around this is to sign out of iCloud Photo and then delete it from your device. This should keep the photos in the cloud as long as they are on another device and free up space in the iPhone.
iCloud photos also have an option in settings to Optimize iPhone Storage, turning this on, if not already on, will reduce the file size and save it to the cloud. I would do a test delete with one photo with iCloud Photos off and make sure it stays on the other device and keep it saved on one device.