Phobos, or Terror, was one of the sons of Ares and Aphrodite. He accompanied his father into battle. Phobos is more of an abstraction than an actual god and does not appear in any Greek myths.
"In the centre was Phobos (Fear) worked in adamant, unspeakable, staring backwards with eyes that glowed with fire. His mouth was full of teeth in a white row, fearful and daunting, and upon his grim brow hovered frightful Eris (Strife) who arrays the throng of men ..."