This is the world portrayed in Spike Lee's movie about phone sex, Girl 6.
At that time independent phone sex was more dangerous, as Lee's movie portrays.
Software platforms were custom written to handle money collection and transfer, connecting caller and sex worker though neither could see anything but the platform's phone number, and metering the connection.
Details vary significantly from one platform to another, but the provider may be given a personal page on the platform to use however she (sometimes he) wishes.
All they have to do is send their recent photos and bio to the site administrators.