Phyllis Hastings was the wife of William Hastings.
While in the zone with Ruth Davenport, William was attacked by several people who grabbed him around the neck and demanded to know Phyllis' name. Subsequently, Phyllis had an arrangement with Dale Cooper's doppelganger.
After Bill could not be released on bail, she was allowed to briefly see her husband in his jail cell. He insisted that he was never in Ruth's apartment, but he had had a nightmare that night of being in her apartment. She then accused him of lying and having an affair with Ruth, which was followed by him stating his awareness of her affair with their lawyer, George, and possibly someone else as well. She gleefully taunted him with "life in prison," then left rather pleased to be rid of Bill. As she was leaving, she informed the arriving George that Bill was aware of their affair, so requested he not walk her out, though they did plan on meeting at her house later that evening.
When she returned home, Dale Cooper's doppelganger was waiting in the living room. He congratulated her, telling her that she "followed human nature perfectly", then proceeded to murder her with George's gun.