He was the commander of Abimelech (King of Gerar)'s army.
Just as Abimelech seems to be a title for a king rather than a personal name, Phicol also appears to be a title for a military commander. He appears in both the time of Abraham and the time of Isaac.
Gen 21:22At that time Abimelech and Phicol the commander of his army said to Abraham, “God is with you in all that you do.
Gen 21:32So they made a covenant at Beersheba. Then Abimelech and Phicol the commander of his army rose up and returned to the land of the Philistines.