Beginning as a non speaking extra, Phyllis was seen in the background of many episodes, with a line here and a mention there.
Her character is never a main one, but she is eventully given more lines. She is often used as a heavy, or used to set someone up, whether she knows it or not.
When Maxine Daniels friend Roxanne Bradshaw plans to sell her baby, Phyllis attempts to dissuade her, revealing her own heartbreak at having to give her daughter up for adoption as a teenager. This is one of the experiences, along with her recidivism and eventual estrangement from her brother that turns Phyllis into a more bitter, villainous character.
On one of Bea Smith's many escapes, Phyllis provided the hair dye for Bea to change her hair colour. Unfortunately Phyllis was later used in a set up to get rid of Bea.
Phyllis along with Mary Adler and several others targeted Sonia Stevens when she was imprisoned, as her husband Eddie was their arresting officer. Her attempts to plash ground glass in Sonia's bed and razor blades in her soap are outsmarted by Sonia, and she is intimidated into taking Sonia's side against Bea.
Phyllis allies herself with Reb against Cass, Minnie and co. for the promise of drugs and other contraband, though Joan attempts to use her to beat Reb. During the escape from the choir group bus, Reb double crosses her, leading to Phyllis taking the driver's young daughter hostage. She later tries to frame Cass and Judy for this.
Eventually Phyllis messes up a scheme by Reb Kean to bring drugs into Wentworth. Reb takes revenge by cornering Phyllis in the shower block bashing her with a wooden statue, causing her brain damage (460).
In episode 580 while confronting Kean, Joan Ferguson mentions Phyllis, saying that "she is a vegetable now thanks to you".