Sanaz Toossi had just cleared security at the San Francisco airport when her cellphone rang at midday Monday. It was her agent, telling the 31-year-old playwright she had won the Pulitzer Prize in drama for “English,” her first produced play.

Toossi, who had written the play as a graduate school thesis project at New York University, was in disbelief. “I asked, ‘Are you sure?’ And when she said, ‘Yes,’ I said, ‘Could you please just double-check?’”

The prize was real, and as Toossi boarded the plane home to Los Angeles, her phone began buzzing with congratulatory messages not only from around the United States, but also from Iran, where her parents were born and where the play is set.

“English,” which Off Broadway’s Obie Awards recently named the best new American play, is a moving, and periodically comedic, drama about a small group of adults in Karaj, Iran — the city where Toossi’s mother is from — preparing to take the Test of English as a Foreign Language. The Pulitzers called it “a quietly powerful play,” and said of the characters that “family separations and travel restrictions drive them to learn a new language that may alter their identities and also represent a new life.”