His father, Antipater the Idumaean, was the close advisor of the Hasmonean king Hyrcanus II, and his mother Cypros was a Nabatean princess.
Both Phasael and Herod began their careers under their father, Antipater, who was appointed procurator of Judea for the Roman Republic by Julius Caesar.
While Mark Antony was in Bithynia about 41 BCE, accusations were brought before him against the two brothers, who were objects of hatred to many Jews, but the shrewd Herod succeeded in obtaining the dismissal of the charges.
Phasael defended the walls, and Herod the palace, thus routing their antagonists, whereupon Antigonus invoked the aid of the Parthian Empire.
In spite of Herod's warning, Phasael allowed himself to be lured with Hyrcanus to the camp of the Parthian leader Barzapharnes under the pretext of peace talks.