Photos clogging up my iPhone

I currently have my iPhone using iCloud photos so that I have my photo library permanently available to me. However I have almost half of my iPhone storage dedicated to the these low res images and it is severely restricting any new apps and docs going onto my phone. I can't even download the latest iOS. I don't want a phone full of photos anymore as I shoot a lot so is there a way to offload the photos to my iMac or to iCloud for storage (I upgraded my iCloud storage to 2Tb some time ago and I've only used a third or so) and crucially NOT LOSE THEM!