Other information on this topic seems to be a bit out of date, before Alexa was able to place calls for the user.
Currently (Feb 2019) the Alexa app prompts the user for their phone number, confirming by text message. Is there a way to access this information? I would expect something similar to accessing a user's location, e.g.
To add an extra wrinkle, ideally I'd like to access this outside of LWA or any other account linking procedure, but just native to the Alexa app as with location.