What can someone learn about you from your phone number?
The answer depends on what other information someone has. Identifiers always depend on context. To a naked man in a tree  the phone number doesn’t carry any information. But to someone with a list of names and phone numbers, some sort of reverse phone number look up, it might tell them your name.
A while back I wrote about area codes and how they are distributed among states. NANPA is publicly posts data that goes into greater detail with central office codes. Using this data, you can look up the first six digits of a phone number and find more specifically where the central office associated with the number is located geographically.
For example, take the phone number 469 863 7090. This is a business phone number, and so you could type it into a search engine and find out exactly whose number it is. But if that weren’t possible, you could look up 469-863 in the NANPA database to find that the number is located in Frisco, Texas. In fact, the number belongs to Sky Rocket Burger. Recommended.
Now people can move around and keep their mobile phone numbers, so any kind of phone look up may tell you about where someone used to be rather than where they are. That could be even more useful.
 A lawyer once told me that his law school professor said that the only thing the interstate commerce clause of the US Constitution doesn’t apply to is a naked man in a tree.