Getting photos from deactivated iphone

So I now use an iPhone X and that device is connected to my iCloud. I also have an old iPhone 6 which has a bunch of photos still on the device. After I transferred to the iPhone X, I think I deleted some photos from my phone not really understanding at the time that I would be deleting them from my iCloud (and this my computer) at the same time. So I lost them. However- these photos are still on my iPhone 6. I am now want to get these photos fro my old phone, but am not sure about the safest way to do it so I do t lose them. I can disconnect old phone from iCloud- connect to internet and email them to myself? Or can I plug the phone into a computer and download them that way. Any thoughts on best way to save these photos and videos. There are quite a lot of them so the most efficient way to get them in my iCloud would be the best.