The phoenix was a mythical bird that originated in Asia. The Greeks believed that the Phoenix come from Egypt. The bird was said to be able to breathe fire but is best known for its ability to be reborn in its own ashes.
It had the ability to live over a hundred years old, before it begins to sit in flames. When the fire died down, the Phoenix would be reborn as a young bird. When it felt its death approaching (every 500 or 1461 years), it would build a nest of aromatic wood and set it on fire, and was consumed by the flames. When it was burned, a new phoenix sprang forth from the ashes. It then embalmed the ashes of its predecessor in an egg and flew with it to Heliopolis (City of the sun). There it would deposit the egg on the altar of the sun god.
From the body of the parent bird, a young Phoenix issues forth, destined to live as long a life as its predecessor. When this has grown up and gained enough strength, it lifts its nest from the treeand carries it to the city of Heliopolis in Egypt, and deposits it in the temple of the Sun.
In ancient Greek and Egyptian mythology, the phoenix is a mythical bird and associated with the Egyptian sun-god Re and the Greek Phoibos (also known as the Greek god of music and light among other things, Apollo). According to the Greeks, the bird lives in Arabia, near a cool well. Each morning at dawn, it would bathe in the water and sing such a beautiful song, that the sun-god stops his chariot to listen. There existed only one phoenix at the time.
In Egypt is was usually depicted as a heron, but in the classic literature as a peacock, or an eagle. The phoenix symbolizes immortality, resurrection, and life after death. In that aspect it was often placed on sarcophagi (Egyptian coffins for the well-respected). It is associated with the Egyptian Benu (the mythical sun bird of Heliopolis that symbolized the rise of life), the Garuda (golden-bodied bird also known as the "Birds of life") of the Hindus, and the Chinese Feng-huang (with the head and comb of a pheasant and the tail of a peacock, these birds represented the personification of the primordial force of the heavens.)
And, of course, I simply can't forget the most famous phoenix of all! Fawkes! Dumbldore's faithful companion, who has saved Harry's ass before and probably will continue to save his pathetic life because Harry is just that stupid and Fawkes is just that cool. 
