How can I recover photos from a stolen iPhone?

If you had iCloud Photos turned on you can use any Internet browser and log into www.icloud.com and go to the Photos app there. You can also turn on iCloud Photos on a new iPhone or other Apple device or Windows PC using iTunes for Windows and the photos will sync with it. See: Set up and use iCloud Photos - Apple Support

If you didn't have iCloud Photos turned on but do have a backup to iCloud or to a computer, you can restore that backup to a replacement iPhone. See: Restore your device - Apple Support

If you had iCloud backup turned on then they will come back on the new device once you completed an iCloud Transfer.

I suggest reading the follow APPLE Help Resources:

1. Use iCloud to transfer data from your previous iOS or iPadOS device to your new iPhone, iPad, or iPod touch - Apple Support
2. Remove a device from Find Devices on iCloud.com - Apple Support