Phaneuf made his international debut for the Canadian junior team at the 2004 World Junior Ice Hockey Championships in Helsinki, earning a leadership role under Head Coach Mario Durocher. A devastating bodycheck to the Czech Republic's Rostislav Olesz led the referee to eject Phaneuf from the semi-final game; he was not suspended, however, and played in the gold medal game. The Canadians lost the final to the United States, while Phaneuf was named a tournament All-Star at defence.