My understanding is that all numbers in the dump correspond with Facebook accounts, so this shouldn't be the reason.

Another option would be that someone else has that number listed for their account. Has Facebook always required confirmation that a number is valid? I saw one my friends' numbers in the data except the account had a different name.

So, that begs the question: If _my_ phone number is in someone _else's_ contacts, is it still _my_ phone number?

It is still PII which sometimes has specific laws and rules around its use depending on where you are.

If I give someone's social security number to a company that doesn't mean they can publish it on the front page just because the person it belongs to didn't hand it over.

It's your phone number (or possibly also the phone number of the person who had it before you) but, like images of yourself, they're probably in tons of places that you don't control and never will.