Which of Plautus' works features a character who assists his master in freeing a courtesan named Phoenicium?

The work of Plautus that features a character assisting his master in freeing a courtesan named Phoenicium is indeed "Pseudolus." In this play, the clever slave Pseudolus devises a series of cunning schemes to help his young master, Calidorus, win the affection of Phoenicium, who is held against her will by a pimp named Ballio. Pseudolus showcases his quick wit and resourcefulness, which are characteristic qualities of many figures in Roman comedy, particularly those found in Plautus' works.

The narrative drives forward with Pseudolus manipulating situations, outsmarting the antagonist, and ultimately enabling Calidorus to rescue Phoenicium. This central plot highlights themes of cleverness and the dynamics between master and servant, making "Pseudolus" a quintessential example of Plautus' comedic style and exploration of social relationships.

The other works mentioned, while notable in their own right, do not focus on this particular storyline involving Phoenicium. "Amphitryon" revolves around themes of identity and deception involving the gods; "Mostellaria" deals more with themes of mistaken identity and family issues; and "Miles Gloriosus" centers on the boastful soldier Pyrgopolon