OK, I'm going to assume you subscribed to IDNotifiy as part of one of the Turbotax bundles, and they notified you about this, and it is not a scam.
However, its not very important, either.
Firstly, this is a Turbotax forum and we specialize in answering tax questions; even though Turbotax offers IDNotify as a paid add-on, we don't really handle those issues. Check their web site for more information.
Second, not too many years ago, everyone's phone number was in a big yellow and white book that everyone got a copy of for free from the phone company, and you had to pay extra to keep your name out of the book. So the idea that your phone number is known by people outside your circle of friends is not new. Even though in the cell phone era it is a bit harder for strangers to get your number, it is not difficult or uncommon. The fact that your phone number is known means that scammers could call you and try to trick you by various schemes. But they could do that anyway with a random dialer, and the best way to discourage scam phone calls is to hang up right away. If you talk to them, your phone number gets tagged as "live", which leads to more calls.
If you really want your phone number to be secret to anyone who is not a confirmed friend or business associate, you can think about calling your carrier and changing it, but that leads to its own kind of disruption.
