The middleweight contender has left team Serra-Longo, his manager Lex McMahon confirmed with MMAFighting.com Thursday.
"He is deeply appreciative of everything that both Matt Serra and Ray Longo have done for him," McMahon said. "However, Costa felt he needed a change to advance his career to the next level.
"He is now training with Keith Trimble at the Bellmore Kickboxing Academy [also on Long Island, N.Y.] and looking forward to his next fight."
Serra added, "he's a good dude and left on good terms. (I) wish him the best on his future fights."
Longo wasn't available to comment on the situation.
Serra first announced the news on Wednesday's MMA Sentinel podcast.
Philippou has been campaigning for a fight against Michael Bisping on Twitter recently, however, McMahon said his client's next fight has not been finalized just yet.
Philippou (12-2, 1 NC) was scheduled to fight Ronaldo "Jacare" Souza on May 18, but he withdrew from the fight due to a cut suffered above his eye. He has won his last five fights in a row.