Pan-Hellenic Sun - The Vergina Sun - (Greek: Ήλιος της Βεργίνας) (also known as the Star of Vergina, Macedonian Star, or Argead Star) is a rayed solar symbol appearing in ancient Greek art from the to centuries BC
The phoenix represents rebirth. It is known when people or things fall and are reborn stronger. The phoenix could e used to describe the novel as a whole. You can see this symbol many times throughout the novel, mainly with Montag.