The tragedy took place around 10 a.m. and involved a pair of single-engine planes with two people inside each; one was registered to Bird Acquisition LLC, which does business as TransPac Aviation Academy.
It's a school for commercial pilots and the company confirmed that the deceased were instructors.
Reasons for the collision remain unknown.
"Both of them collided. We don't know how or what," said Phoenix Fire Department Capt. Larry Nunez. "The skies are clear."
An investigation is underway, but it may take months to reach a conclusion.