Hopefully your dad syncs his phone with iTunes every night. If he does, then you can...
Connect the iPhone to his computer, run iTunes.
Once iTunes loads the phone, right click on it and select Restore from Backup.
Then select the latest backup (look at the time and date next to them to determine the latest one).
Then let it be.
Now depending on how much stuff (apps, pics, songs etc.) he had on the phone, it could take a while. Maybe an hour or so.
Good luck and next time be careful playing w/ phones. It's one sensitive and important device we use these days.
