According to Wikipedia
A phone sex worker is a type of sex worker and pornographic actor, sometimes referred to as “phone actor,” “fantasy artist,” “adult phone entertainer,” “audio erotic performer,” or any one of other monikers. The most valued attributes of a phone sex professional are his or her voice, acting and/or sexual roleplay skills, along with the experienced ability to discern and respond appropriately to a broad spectrum of customer requests.
What phone sex workers often do involve taboo topics that paying customers cannot engage in during real life sexual encounters due to moral and legal ramifications, psychological inhibition, lack of physical ability, unwillingness of a committed partner or the fear of social stigma. Phone sex operators or companies may, by policy or discretion, refuse to entertain certain requests. Many other services accommodate the extreme taboo market by using signifying phrases in their advertising such as “no taboos” or “no restrictions.”
Phone sex services primarily market to men or women of a particular sexual orientation, and focus on mainstream sexual experiences. Specialized companies also cater to clients who have a certain sexual predilection (e.g., zoophilia, coprophilia, domination/submission, humiliation) or an erotic interest in a specific group (nurses, doctors, firemen, college students, older/younger figures, ethnic minorities, etc.) It is not at all unusual for a phone sex service to employ a staff of phone sex performers to meet both mainstream and exotic customer requests.