Twitter needs to stop pressuring users to add their phone numbers to their profiles and stop defaulting to making those phone numbers discoverable. eff.org/deeplinks/2020…
Until then, here's our guide to changing your settings to protect, or just remove, your phone number on Twitter. eff.org/deeplinks/2020…
First, head to the "Privacy and safety" section of your account settings, then scroll down a bit and select "Discoverability and contacts"—or just go to twitter.com/settings/conta…. 
You want “Let people who have your phone number find you on Twitter” unchecked. (And while you’re at it, make sure “Let people who have your email address find you on Twitter” is unchecked, too.)
Note that, unless you are in the EU where the GDPR requires that features like this be opt-in, these are both checked by default.
To check whether or not you have a phone number associated with your account, go to the "Account" section of your settings and select "Phone"—or just go to twitter.com/settings/phone.
If you see a phone number there that you do not want associated with your profile, click "Delete phone number."
