You can keep your phone number private with the introduction of the Signal

WIRED 5/10: Phone Number Privacy for a Low-Precision, Low-Sensitivity Message on the App Store

The new features that are part of the roll out are described as “phone number privacy.” Those features, which WIRED has tested, are designed to allow users to conceal their phone numbers as they communicate on the app and instead share a username as a less-sensitive method of connecting with one another. Rather than give your phone number to other Signal contacts as the identifier they use to begin a conversation with you, in other words, you can now choose to be discoverable via a chosen handle—or even to prevent anyone who does have your phone number from finding you on Signal.

The app will also start hiding your phone number by default if users don’t already have it saved in their phone. If you want to change this, head to your settings and choose Privacy > Phone Number. Someone can see my number. You may have to wait a few more weeks for the features if you have the regular version of the app.