8 But the Greeks ask for a resurrection of the dead still manifest; and say that, even if these creatures are raised, yet they had not utterly mouldered away; and they require to see distinctly some creature rise again after complete decay. God knew men's unbelief, and provided for this purpose a bird, called a Phoenix. This bird, as Clement writes, and as many more relate, being the only one of its kind, arrives in the land of the Egyptians at periods of five hundred years, showing forth the resurrection, not in desert places, lest the occurrence of the mystery should remain unknown, but appearing in a notable city, that men might even handle what would otherwise be disbelieved.
For it makes itself a coffin of frankincense and myrrh and other spices, and entering into this when its years are fulfilled, it evidently dies and moulders away. Then from the decayed flesh of the dead bird a worm is engendered, and this worm when grown large is transformed into a bird—and do not disbelieve this, for you see the offspring of bees also fashioned thus out of worms, and from eggs which are quite fluid you have seen wings and bones and sinews of birds issue. Afterwards the aforesaid Phoenix, becoming fledged and a full-grown Phoenix, like the former one, soars up into the air such as it had died, showing forth to men a most evident resurrection of the dead.
The Phoenix indeed is a wondrous bird, yet it is irrational, nor ever sang praise to God; it flies abroad through the sky, but it knows not who is the Only-begotten Son of God. Has then a resurrection from the dead been given to this irrational creature which knows not its Maker, and to us who ascribe glory to God and keep His commandments, shall there no resurrection be granted?
Source: Catechetical Lectures (New Advent)