Often, when a user gets a new mobile device, they will be unable to log into their Salesforce instance until they set up the Salesforce Authenticator app on their new device.

Why can I no longer use the Salesforce Authenticator app to log into Salesforce?

You will need to raise this concern with your system administrator and give them the following instructions:

1. Go to Setup >> Quick Find: Users >> Users
2. Go to the user and click on the user's name
3. In the left column, scroll down to App Registration: Salesforce Authenticator
4. Select the [Disconnect] link

Once done, you should be able to set up the authenticator app on your new phone.