The Phonix D.I was a single-seat biplane fighter with a stout and compact design, used by both branches of Austro-Hungarian air service. It was a fast airplane, well-armed and offering good vision, but it was quite difficult to maneuver and had a poor climb rate. Employed first as an escort fighter and fighter, in spite of structural weaknesses, it was favorably received by many pilots, who found it stable, robust, and easy to fly. The D.I was also used effectively as a photo-reconnaissance aircraft.

Phonix D.I (Lang)
Scoring his last three victories against Macchi seaplanes, Friedrich Lang became one of only two naval aces of the Austro-Hungarian Empire.