Phrontis and his brothers were raised in Kolkhis, but after their father died, he and his brothers set out to avenge their father’s ill treatment in the hands of king Athamas of Orchomenus and were stranded on the Island of Ares the War God in the Black Sea until they were rescued from the island by the Jason and the Argonauts. Once Jason received discovered that Phrontis and his brothers were grandsons of King Aeëtes of Colchis, Jason convinced Phrontis and his brothers to return with him to Colchis and help him to obtain the Golden Fleec. Jason also questioned Phrontis and his brothers on the layout and security of the land. After the Fleece was retrieved from Colchis, Phrontis and his brothers returned with the Argo's crew to Greece. His brothers were Kytissorus, Phrontis and Melas , and, according to some accounts, Presbon was another one of his brothers.
When the Argonauts had entered the sea called Euxine through the Cyanean Cliffs, which are called Rocks of the Symplegades, and were wandering there, by the will of Juno they were borne to the island of Dia. There they found shipwrecked men, naked and helpless – the sons of Phrixus and Chalciope – Argus, Phrontides, Melas, and Cylindrus. These told their misfortunes to Jason, how they had suffered shipwreck and been cast there when they were hastening to go to their grandfather Athamas, and Jason welcomed and aided them. They led Jason to Colchis, bade the Argonauts conceal the ship.
- Hyginus, Fabulae, 21