Stolen phone

If you were syncing photos to iCloud on the stolen phone, have you signed into Settings/Your Name/iCloud on the new phone using the same Apple ID, and turned Photos syncing on? The photos sync is very, very slow. Depending on how many photos you had, it could take a couple of weeks or more to complete the sync.

If you weren't syncing photos with iCloud, do you have a backup you can restore from? Restoring from a backup erases all data currently on your device. Any data newer than when the backup was made will be erased. A restore is an all or nothing restore. You can't access a backup and only restore certain files.

Backup - Restore your device from an iCloud or iTunes backup.    

Why do you want to change the password? That may interfere with accessing the data from the stolen phone.

You don't need the stolen phone to do what I posted above.