I accidentally backed up my iphone with another phone, what can i do to get back my photos and contacts?

You can't backup one iPhone with another iPhone. The backup for each iOS device is created and stored separately.

Do you mean you restored your iPhone with iTunes with the backup for another iPhone?

The backup for each iOS device is created and stored separately.

When restoring an iPhone with iTunes when there is more than one backup available, you can select the backup you want to restore the iPhone with. Restore the iPhone with iTunes again and this time select the correct iPhone backup when prompted.

If you never backed up the iPhone before restoring the iPhone with iTunes (you are prompted to create or update the iPhone's backup as the first step when selecting Restore when the backup is created and updated locally on your computer vs. backing up the iPhone wirelessly with an iCloud account), you are out of luck.