Phillipa Saint was interested in sex long before she ever had any.
An avid reader all her life, Phillipa got interested in erotica in her late teens. Very interested.
So interested that her mind began to fill with fantasies and sexual scenarios.
So she began researching sex and pleasure. Specifically, how to please both her (eventual) partners and herself.
When she did have sex, she got no complaints and plenty of compliments. Which makes her assume her research was well done.
However, Phillipa wasn't writing yet. She always was a writer. Stories always fascinated her as much as sex, and she always made up elaborate ones about her favorite subjects. But she never had the courage to write them, because she assumed she wouldn't be any good at it.
Then a major romantic disappointment happened, and Phillipa decided it was time to change. No more fears, no more hiding or running from who she was.
So she wrote her stories. And then wrote stories about sex. And kept doing it.