How to recover lost iPhone iCloud photos?

If you use iCloud Photos, your photos are also saved directly in iCloud and you can copy them from there to your computer. Have a look at this article:

Archive or make copies of the information you store in iCloud - Apple Support

If you buy another iPhone, set it up with the same Apple ID and enable iCloud Photos again on that device, all your photos in iCloud will sync back.

Log in at iCloud.com/photos. Anything that had synced before you lost your device will be in the cloud.