As an autonomous remote-bombing device, the Phoenix is capable of delivering staggering amounts of ordnance to a specific target. Hold the Target Painter beam on an object or ground point until it signals target lock. An immediate air strike follows with the Phoenix releasing its payload directly, if indiscriminately. Held aloft by four pulse-ramdrive engines, and plated in Duranium armor, the heavily armored Phoenix is ponderous, but effective in combat. The Phoenix makes it presence felt on the battlefield briefly, although a vigilant Raptor pilot or Stationary Turret gunner has been known to take them down.
-- Official description

While the player cannot control the Phoenix, that doesn’t mean it isn’t very dangerous. The Phoenix is called with the Target Painter, and when it arrives, it delivers an air strike by dropping several powerful bombs on the target. It arrives from end of the map, heads to the target, drops it’s load, and then flies away. If an enemy sees a Phoenix, he can shoot it down with the AVRiL, and one shot is enough to destroy it. Enemies can also fire it with a turret, or from a Raptor.