Phyllis Ann Karr was born Karmilowicz in Oakland, California, and shortened her suname. Her literary interests encompass Arthurian legend, Shakespeare, the works of Gilbert and Sullivan, and the Oz books of L. Frank Baum. In the 1970s, she began publishing articles, poetry, and fantasy and mystery stories in periodicals and journals such as Ellery Queen's Mystery Magazine, Weird Tales, The Savoyard, and Library Review. Her earliest novels were romances, but she then began to write fantasy and mystery novels, including the Frostflower series and The Idylls of the Queen: A Tale of Queen Guenevere (1982). Between 1986 and 2001, she concentrating on shorter works. Many of her stories have been anthologized. Her major nonfiction work is The King Arthur Companion (1983), later expanded as The Arthurian Companion (1997). She married Clifton Hoyt in 1990.