Good comment. Why do people care if their phone number gets leaked? There use to be a yellow page book with everybody’s phone number. Also, phone numbers are not identities. I change phone number every year on average.
It's the most identifiable thing about me other than my social security number. Even my driver's license number has changed more than my cell phone, and I don't always have a valid passport.
Determined person can use the various leaks and other data sources to collect more detailed profile of you (and millions of others). This will eventually allow them to setup more targeted and personalized spam or phishing campaigns.