Because, though the phoenix burns in a fire of its own making, it rises again from the ashes.
And though the phoenix is a mythical being, its image has surfaced across cultures and through the centuries for a reason - if this is what people need to believe, they could do much worse, and it really is very strong symbolism. Like Mom says, "Everything works out in the end, and if it doesn't work out, it's not the end."
(p.s. - thanks, Greg - still love the design!) :)