That's not how you're supposed to do it, and as long as you have iCloud space (or don't mind paying for enough space) you should let them all in iCloud.

If you have iCloud Photos enabled, your photos should all upload in full quality to iCloud, and then your phone is able to get rid of the full versions and just keep thumbnails in your Photos (if your phone needs the space) so that if you go to look at older photos, you'll have a momentary pause while it downloads the full version seamlessly.

There's no reason to mess around with getting them off your phone onto a computer and manually do any of that -- unless you don't have space in iCloud.

Your phone will basically keep as many photos in full quality as it can based on available free space, but they can be purged at any time because it will just download the full version again if you open it.

If you have to jump through hoops like these to write papers, then you're doing it wrong.

Sorry luv.

Just because you can doesn't mean you should.