Recovering pictures from stolen iPhone via iCloud

If you had iCloud Photos turned on, the photos would have automatically synced with iCloud when they were taken if Internet was available. You can use any internet browser and log into www.icloud.com and go to the Photos app there to view or download the photos.

Also see: Set up and use iCloud Photos - Apple Support

If you didn't have iCloud Photos turned on but did have iCloud Backup turned on, the photos might be there, but note that iCloud Backup only happens periodically (when the phone is charging and connected to wi-fi or when you do a manual backup).

You can restore the entire backup (not just the photos) from iCloud to a replacement or other device but you cannot otherwise view the contents of the backup. The following Apple article has information about backup: Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

Photos uploaded on reconnection?

Probably not.

I’d assume anything not already uploaded is gone, and that the device reset takes priority.

Though probably already familiar, here is what to do: If your iPhone or iPad was stolen - Apple Support

Whether your passcode was also compromised, or whether stolen device protection was active, can also alter the potential outcomes here, beyond the photos.