A New Hope
They where sent to Tatooine by Darth Vader to search for a escape pode with a R2 unit and a droid assistant who has the blue prints for the Death Star. While on the planet Tatooine they attacked and killed a Jawa transport, Uncle Owen and Aunt Beru. Before being mind tricked by Obi Wan Kenobi and nearly caught the Millennium Falcon.
The Sandtroopers were on Tatooine looking for the Death Star plans. They shot at Phineas, Ferb and Isabella as they were leaving.