Autopilot sends the user's phone number as a parameter (
UserIdentifier) of the Task's HTTP Callback.
You can find all the parameters Autopilot sends here:
Is it possible to access the user's phone number as a variable of the Actions JSON in the Actions Bin?
Unfortunately not at this point. If you need the user's phone number you have to configure the Task with an HTTP Callback and get it as a parameter of that request in your application or Twilio Function.
Yes, you can learn more about the Autopilot Studio Widget in the links below: