In the 2011–12 season, his second professional season, he played 30 games for Phantoms Braunschweig, averaging 2.3 points, 0.7 assists and 0.8 rebounds in about 8 minutes per game.
In the 2012–13 season he played 32 games for Phantoms Braunschweig, averaging 12.0 points, 3.2 assists and 2.5 rebounds in about 25 minutes per game. For the season, he was named the League's Most Improved Player as well as Best Young German Player.
In 2013, Schröder was announced to play at the 2013 Nike Hoop Summit for the World Select Team. Before officially playing at the Nike Hoop Summit, Schröder decided to declare for the 2013 NBA Draft. On April 20, 2013, Schröder led his team to a 112-98 win. He finished with 18 points, 6 assists and 2 rebounds in 29 minutes.
Schröder is the son of a German father and a Gambian mother. He stated that he started focusing on his basketball career after his father died in 2010. He and his brother were both heavily involved with skateboarding until Dennis found basketball at age 11. His agent is former German basketball national player, Ademola Okulaja.