Phobos (Ancient Greek: Φοβος, meaning "fear") was the Greek god of fear in Greek mythology. He is the offspring of Aphrodite and Ares. He was known for accompanying Ares into battle along with the ancient war goddess Enyo, the goddess of discord, Eris (both sisters of Ares), and Phobos' twin brother Deimos, god of terror.
Homer, Iliad 4. 436 ff (trans. Lattimore) (Greek epic C8th B.C.) :
"Ares drove these [warriors] on . . . and Deimos (Terror) drove them, and Phobos (Fear), and Eris (Hate) whose wrath is relentless, she the sister and companion of murderous Ares."
Homer, Iliad 5. 738 ff (trans. Lattimore) (Greek epic C8th B.C.) :
"Across her [Athena's] shoulders she threw the betasselled, terrible aigis (aegis), all about which Phobos (Terror) hangs like a garland, and Eris (Hatred) is there, and Alke (Battle Strength), and heart-freezing Ioke (Onslaught) and thereon is set the head of the grim gigantic Gorgo (Gorgon), a thing of fear and horror, portent of Zeus of the aigis."
[N.B. The daimones (spirits) imbued the aigis with its power.]
Homer, Iliad 11. 36 ff :
"[The shield of Agamemnon:] And he took up the man-enclosing elaborate stark shield, a thing of splendour. There were ten circles of bronze upon it, and set about it were twenty knobs of tin, pale-shining, and in the very centre another knob of dark cobalt. And circled in the midst of all was the blank-eyed face of the Gorgo (Gorgon) with her stare of horror, and Deimos (Fear) was inscribed upon it, and Phobos (Terror)."
Homer Iliad 13. 298 ff :
"As Ares is when he strides into battle and Phobos (Terror) goes on beside him, his beloved son, the powerful and dauntless, who frightens even the patient-hearted warrior: these two come out of Thrake to encounter in arms the Ephyroi or the great-hearted Phlegyes, but the two will not listen to prayers from both sides, but give the glory to one side or the other."
Homer Iliad 15. 119 ff :
"So he [Ares] spoke, and ordered Deimos (Fear) and Phobos (Terror) to harness his horses, and himself got into his shining armour."
Hesiod, Theogony 933 ff (trans. Evelyn-White) (Greek epic C8th or C7th B.C.) :
"Also Kytherea [Aphrodite] bare to Ares the shield-piercer Phobos (Panic) and Deimos (Fear), terrible gods who drive in disorder the close ranks of men in numbing war, with the help of Ares, sacker of towns."