His short reign was mainly marked by his war with the Seleucid Empire, which under king Antiochus VII Sidetes (r. 138–129 BC) attempted to regain the lands lost to Phraates' father.

Initially unsuccessful in the conflict, Phraates II managed to gain the upper hand and defeated Antiochus VII's forces, with the Seleucid ruler himself dying in battle or committing suicide.

He was succeeded by his uncle Artabanus I. Phraátēs (Φραάτης) is the Greek form of the Parthian Frahāt (𐭐𐭓𐭇𐭕), itself from the Old Iranian *Frahāta- ("gained, earned").

[2] Phraates II was born in c. 147 BC; he was the son of Mithridates I, the fifth Parthian king, and a noblewoman named Rinnu, who was the daughter of a Median magnate.

Then, time having gone by… he [Demetrios] took flight again with the same friend as companion, with equal misfortune, he was seized near the borders of his kingdom, and conducted again to the king who regarded him with ill will; he was removed from his presence.

Thereupon, as a grant to his wife and children he was sent back to Hyrcania, the city of his [former] imprisonment…[9]Antiochus, well-aware of Phraates II's plan to use his brother against him, invaded the Parthian realm in 130 BC to thwart it.

[17] Phraates II also released Demetrius, who had been held by the Parthians as a hostage for several years, to become king of the Seleucid realm for a second time.

[25] Like his father, Phraates is depicted on coins wearing a Hellenistic diadem, whilst his beard represents the traditional Iranian/Near Eastern custom.