title: Link multiple authentication providers for phone and email
body: <p>I am new to firebase so please be patient with my question following:</p>
  
  <p>User are able login to my apps using phone authentication or email, but it will generate two different UID for a same user, what I wish to achieve is one user with one UID can login with email or login by phone number (<strong>Merge the phone number and the email in authentication</strong>). May I possible to achieve this at Firebase? </p>
  
  <p>thank you</p>
  
  <p><a href="https://i.stack.imgur.com/NMvmr.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/NMvmr.jpg" alt="Problem of one user with two user UID"></a></p>