Phyllida Campion is a non-canonical character created for the 1993 film adaptation of The Case of the Missing Will in Series 5 of ITV's Agatha Christie's Poirot. She is the principal of a woman's college at Cambridge University. She is also a close personal friend of the wealthy Andrew Marsh. His ward, Violet Wilson is one of her students.
In investigating the murder of Andrew Marsh, Poirot ultimately revealed that Violet Wilson was Andrew's daughter, the offspring of a union with Phyllida. This had happened in 1913, when she was still a student at Cambridge. Andrew was presumably also a student and this was also probably just before he departed for Australia. Sarah Siddaway had killed Andrew to prevent this fact emerging and forestall the possibility of Andrew changing his will to favour Violet. When Sarah overheard that Phyllida was going to London to see Poirot, she feared that Phyllida was about to reveal Violet's true parentage to him. Sarah followed Phyllida to London and tried to kill her by pushing her down the escalator at a London tube station. Fortunately Phyllida survived. It was during her treatment at a hospital that doctors discovered that she had once had a child by the caesarian section. Following up on this, Poirot sent Miss Marple to a cottage hospital (presumably near Cambridge) where she was able to retrieve the birth record proving that Violet was Phyllida's and Andrew's daughter.
Phyllida Campion is portrayed by Susan Tracy. What college she is principal of is not mentioned but in the original story, Violet went to Girton College.