It is unknown when the Phoenix Gundam was developed, and for what purpose. It is equipped with a wide variety of weapons, including a pair of beam sabers and beam rifles, four mega particle cannons located in the wings, and a set of remote controlled "Feather Funnels". It can also transform into a bird-like Mobile Armor mode.
Its name came from its "Burning Fire" attack, which involves it transforming into its MA form and enveloping its entire body in energy, similar to the legendary phoenix, before ramming into its opponent.
Uniquely, the Phoenix is equipped with Nanoskin Armor, allowing it to repair itself to an extent. Though this feature is inert while the Phoenix Gundam is not at its Full Power state.
There are many unsolved mysteries surrounding the Phoenix Gundam. It has no maintenance hatch on its surface, apparently since its Nanoskin Armor was supposed to maintain itself. It is capable of long distance flight without using propellant. Also, it apparently contained technology from multiple different timelines.