It's not about porn specifically, but at one point you gave your phone number to a company. Could have been for anything, usually it's for "verification" or 2fa on a new account on any number of types of service. Then that company turned around and sold your phone number to a data broker - or, worse, was hacked and the hacker then sold their ill gotten gains to said data broker. Who then sold that number to a different company, who then sold that number to a different company...

This is why knowing where your data gets around to is important. If your phone number can (and most assuredly does) get passed around town like a cheap hooker, imagine what kinds of transactions are being performed on, say, email addresses. Or social security numbers. Or passwords, or security question answers. Trusting the wrong data into the wrong hands, once, will mean that data is now permanently a matter of public record. Oh, Equifax leaked your phone number? Now every single illegal data broker in the entire world has a copy of that information in their database, there are 3800 additional copies in various hackers' personal data stores, and new copies are being sold to new people every day. Whoops, now Netflix leaked your email address, hackers already have your name and phone number to link to it from Equifax, oh no, that's a complete data profile. Someone can now just buy your data profile to either target you with ads or target you with scams, or worse. Oh no, you got got by one of the targeted scams and accidentally gave your SSN to a bad actor - well, hope you're already on the way to the courthouse because your identity is now unusable. Whoever you were previously is now dead. You've just made appearances in Pripyat, Brazil, Bangladesh and 13 locations in China in the last 8 minutes and made credit card purchases at each location, your 401k is now smoke and your bank accounts are throwing the emergency halt lever. You'll be lucky to recover anything at all after legally changing your name and SSN, which is a real bitch to do, and will only get more difficult over time as Republicans grow increasingly terrified of the existence of trans folks.

Anyway, yeah, moral of this story is, this is why some people are so vocal and up in arms about data privacy issues and laws, be careful who you give your data to because it can and will be used against you to great effect by multiple prongs of malicious actors, change your passwords frequently and for the love of god don't give out your SSN unless it's absolutely required and you know for a fact it's going directly to a governmental agency.