How do I delete photos off my iPhone ONLY and leave them in iCloud

You can’t. iCloud is a syncing service, not an archiving service. If you don’t want to keep them on your phone you need an archiving service, such as Google Photos, Dropbox, box.com, shutterfly, Microsoft OneDrive, Livedrive, etc. All of these have apps for your iPhone that will archive automatically.

You cannot. iCloud photo is a synchronization service. Any changes made will be reflected in what is in iCloud.