Formerly a First Lieutenant, Sean Phillips was demoted to the rank of Private Second Class because of his wolfish advances to a female superior officer. He is with the 15th Alpha Tactical Armored Corps (ATAC) squadron and expert pilot of the Spartas veritech tank. He was the cocky playboy commander of 15th ATAC Squad until busted to Private Second Class for conduct unbecoming of an officer. He fell for and married Marie Crystal, ace pilot of the Tactical Armored Space Corps. He was left behind on Earth following the Invid invasion.

Sean Phillips was highly skillful of the VHT-1 Spartas Hover Tank. He however, was a perennial flirt, and due to his nature, was demoted to Private Second Class. He didn't have a personal problem when Dana Sterling ran things, however. Things change when he starts falling for ace pilot Marie Crystal. By the end of the war, Sean Phillips grows to be a more capable individual.
