Phyllis Curtin, an American soprano celebrated as a champion of new music, died on Sunday at her home in Great Barrington, Mass. She was 94... A mainstay of the New York City Opera in the 1950s and ’60s, Ms. Curtin was noted for the purity of her voice, the sensitivity of her musical phrasing and the crystalline perfection of her diction. On the opera stage and in recital, she gave the premieres of dozens of works by 20th-century composers — “more first, and last, performances than any singer in history,” as she was fond of saying, ruefully...