The Brazilian, who joined the Reds from Inter Milan in January, set up numerous chances for his teammates and also struck the crossbar with a shot from distance.
"Philippe Coutinho was a little genius on Saturday. He had previously shown glimpses of what he can do but against Chelsea the week before he had struggled. They got tight on him and he couldn't get into the game," Aldridge told the Liverpool Echo.
"He bounced back at St James' Park with his best performance for the club and he was my man of the match. Coutinho was given so much time and space and took full advantage. I don't know what Newcastle were playing at."
Coutinho has made 10 appearances for Liverpool, scoring two goals in the process.