The phoenix was a creature from the planet Meteos. The creature was most commonly seen in the form of a bird with red and orange feathers, a featherless head, a yellow beak, long sharp claws and a body bathed in fire. However, that was only a part of their long-life cycle of repeated re-birth. They lived by feeding off energy – light, heat, sound and even thought.
They consumed all the energy they could before they reverted into a shapeless mass, waiting until they found a new food source, from which a new egg was created and hatched. Believed extinct, the Phoenix had destroyed their own planet through their own greed and were forced to drift in space.
One arrived in Arabia on Earth, where it became the source of myth and legend, but was destroyed before it could consume the planet. Another appeared in the TARDIS but was tricked into leaving by the Doctor. It resumed its flight in the Vortex in search of a new energy source. (PROSE: The Bird of Fire)