In the Iliad, he along with his brother Helenus led a group of soldiers at the siege of the newley constructed Argive wall and killed many along with wounding the hero Achean Meriones. As Hector was fleeing Achilleus, Athena took the shape of Deiphobus and goaded Hector to make a stand and fight. Hector thinking it was his brother listened and threw his spear at Achilleus. When the spear missed Hector turned to around to ask his brother for another spear, but Deiphobus had vanished, it was then Hector knew the gods had decieved and forsaken him and he met his fate at the hand of Achilleus.
After the death of Paris, Deiphobus was given Helen as a bride for his deeds in the war, beating out his other brother's bid for her, Helenus. Some accounts say the marriage was by force. When the Trojan Horse was in the city Deiphobus accomponyd Helen as she called out the names of the Greek names in the voice of their wives as she walked around the horse in an attempt to see if the Argive forces were hiding in the horse. Menelaus and Odysseus had to hold the men inside back from responding. During the sack of Troy Deiphobus was slain by either Odysseus or Menelaus and his body was mutilated. Some accounts say it was Helen who killed him, or that she celebrated his death. Most accounts seem to indicate that unlike her other two husbands, Helen didn't love Deiphobus, and decided she would rather return to Menelaus.
See: Iliad books XII, XIV, XXII.
In Virgil's Aeneid, Deiphobus appears in the Underworld to Aeneas. He tells Aeneas the story of his death, which entails Helen's betrayal in signaling Menelaus to Deiphobus' bedchamber. He was mutilated in the sack of Troy. While with Aeneas, he begs the gods for revenge against the Greeks.