A pheonix is a mythical bird blows up into fire and then regenerates itself from its own ashes. Basically the pheonix symbolizes rebirth. It symbolizes how past generations are destroyed by book burning. People have to start all over again once books have been burned. It also symbolizes fire.
The salamandar is a creature who can withstand great heat. It symbolizes Montag's life because he burns things for a living and enjoys it. He basically lives in fire and still stays alive.