I cloud space
To free up space on my Icloud should I delete photos and videos on my I-phone - and will that delete and free up space on Icloud? Or do I need to delete them on both devices to free up space on phone and I-Clooud?
Once you delete photos from a device or iCloud, they are deleted everywhere (all devices). If you wish to manage your iCloud storage space -- Manage your iCloud storage - Apple Support.