Phillips was born as Gladys M. Cassell on 14 November 1912 in Erie, Pensylvania to Lawrence and Julia Cassell. She attended Central State University in Wilberforce, Ohio, and was a member of Delta Sigma Theta, a sorority for African-American women.
Phillips worked as a teacher in Cleveland, Ohio, and was an avid churchgoer known for being active in her community. In August 1952, aged 39, she married Alvin Phillips; their marriage lasted 50 years before Alvin’s death in 2002. The couple had no children, but they had many nieces and nephews.
Phillips died on 5 February 2023 in Richmond Heights, Ohio at the age of 110 years, 83 days. Her funeral was held five days later. She was survived by her brother-in-law Dr. James L. Phillips and his wife Barbara, as well as their descendants.
Phillips was not known to researchers until after her death, when several obituaries were published.