The Phönix C.I was the first original design developed by the Phönix Flugzeug-Werke It was based on the Hansa-Brandenburg C.II that Phönix was building under licence. A conventional biplane with a rear fuselage/tailplane similar to aircraft designed by Ernst Heinkel. The C.I had a fixed tail-skid landing gear and was powered by a 171.51 kW (230 hp) Hiero 6-cylinder inline piston engine, it had two tandem open cockpits for the pilot and observer/gunner. The company built 110 C.Is and then entered service with the KuKLFT in early 1918. After the First World War 30 aircraft were built by the Swedish Army engineering department fitted with 220 hp (164 kW) Benz Bz.IV inline engines.
Phönix C.I aircraft built by Phönix were serialled from Phönix C.I 121.01 to Phönix C.I 121.160 and Phönix C.I aircraft ordered from Lloyd (Ungarische Lloyd Flugzeug und Motorenfabrik AG) were allocated serials from Phönix C.I(Ll) 49.01 to Phönix C.I(Ll) 49.100. Some 80 aircraft ordered from UFAG were not assigned serial nos, probably due to production being interrupted by the Armistice and 225 more were ordered but not built.