title: How do I update a FirebaseUser's phone number in firebase_auth?
body: <p>In my Flutter app I use Firebase's phone number authentication as my main form of authentication. After authenticating, I create a user in my <code>users</code> collection with these details:</p>
  
  <pre><code>{
      phoneNumber: FirebaseAuth.instance.currentUser().phoneNumber,
      displayName: 'Comes from user textbox',
      ...
  }
  </code></pre>
  
  <p>But say one day a user want's to change their phone number. How do I do this? Because I cannot simply change the user's phone number in the document, because the phone number needs to be authenticated. And after authentication, the user gets a new authUID. Which should then be a new user?</p>
  
  <p>Could someone explain the logic behind a user that wants to keep their profile details but change their number.</p>