http://gta.wikia.com/Phoenix
The Phoenix may occasionally spawn around the docks, near the drop-off point for Simeon's missions.
One can also be obtained online by playing the No Hay Bronca mission given by Gerald. The gang leader flees in a Phoenix and is chased into the LS River and gets out at the end. Once he is out, distract him, get in the car, end the mission, and go to freemode. You will be in the Phoenix and are now free to do what you please.
Voir aussi : http://www.youtube.com/watch?v=FKyuaCS2R0E