The Phoenix is, of course, a mythical bird that sets itself afire and rises from the ashes. It is also supposed to be a bird of exceptional beauty. Books are burned in the novel, but there is some hope that they will rise from the ashes, through the efforts of a few good people who carry them within. And books are things of great beauty, too, in so many ways. It is really a wonderful symbol for this purpose, carrying with it hope, renewal, beauty, and a sort of redemption.