In Ray Bradbury's "Fahrenheit 451," the phoenix symbolizes the cyclical nature of mankind's self-destruction and resurrection or re-emergence. This parallel is drawn by Granger, following the city's bombing. The phoenix can also be taken as a symbol for the personal or spiritual rebirth of the novel's protagonist, Guy Montag.
Guy Montag, despite his initial enthusiasm for his work as a fireman, which his father and grandfather were also engaged in, comes to feel restless and is described in the novel as a "fireman turned sour." His dissatisfaction is not confined to his professional role and spills over into his personal life and unfulfilled marriage to Mildred.
His apathy naturally extends to his role in society at large, and to the role of that society in the world, which he deems to be negative, especially when he is forced to burn an old woman to death, along with her books.
The phoenix is the symbol of firemen in Bradbury's fictional dystopia, yet it becomes something more meaningful for Guy Montag following his contact with Professor Faber and, eventually his confrontation with Captain Beatty. Following his captain's defeat, Montag witnesses the destruction of society. Like the mythical phoenix, both he and, figuratively, mankind, emerge from the ashes to rebuild anew.