Phelan was overseeing his first match since signing a permanent deal with the Tigers, but three goals in either half from the Cherries saw them make it an occasion to forget.
Phelan had some strong words for his side after the game, insisting that his players need to "grow up" if they are to stay in the Premier League this season.
"I feel very embarrassed. I've got a team here who show what they can do when they want to," he told reporters.
"We've got to grow up. Unless we concentrate and be disciplined, we won't get to where we want. What we've done today is not good enough."
Hull are now winless in their last six league games, picking up just one point from a possible 18 in that time.