She was often credited as Phyllis Douglas.
Born the daughter of director Ridgeway Callow, Boyce was one of the last surviving cast members of Gone with the Wind, in which she appeared, at the age of two and uncredited, as Bonnie Blue Butler (along with Cammie King).
She also appeared in two episodes of the original Star Trek television series: "The Galileo Seven" and "The Way to Eden" and in a two-parter of the TV series Batman.