This slender, willowy actress with hooded eyes and chiseled cheekbones has demonstrated her versatility in roles ranging from the bon vivant of Herbert Ross' musical remake of "Goodbye, Mr. Chips" (1969) to the bloodthirsty Livia in "I, Claudius" (BBC, 1976) to impersonating screen legend Marlene Dietrich on stage in the 1990s. Sian Phillips began her career as a child performer on the radio in her native Wales. She also did a stint as an announcer and newsreader in her early 20s before concentrating on an acting career. Almost from the outset of her stage work, she was landing major roles,