iCloud media syncing

I recently deleted thousands of pictures/videos to free up space on my iPhone. I then went on to iCloud to see if my back up was still there. The items were sitting in my recently deleted folder so I restored all 17K of them. Is it possible to delete from my device and for it not to affect my iCloud? I deleted on my iPhone and stopped the photo sync, now I am scared to put it back on incase it deletes all the media again? Can someone please explain… I would like to keep all the media external from my phone, does this need backed up in a different way e.g. USB stick or can this be done on iCloud?

Thanks in advance,

Martin