title: Firebase users setting phone number
body: <p>I have been authenticating user from facebook on firebase but i want to make them set their phone numbers linked to the user but i cant find any way to make them set their phone number i can only retrieve using FirebaseUser user.getPhoneNumber and update phonenumber needs credentials not string which i don't know how to use so can anyone help me ?!</p>
  
  <pre><code>FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
  user.getPhoneNumber();
  </code></pre>
  
  <p>user.updatePhoneNumber();</p>