The GET /users/{userId} endpoint returns all phone_numbers for a given user.
The GET /users endpoint does not return any phone_number for the users.
Thus, at the moment, to retrieve the mapping user → phone_number, one needs to first call GET /users to fetch all userIds, and afterwards call GET /users/{userId} N times (N = number of users in your account).
We would benefit greatly from the GET /users endpoint also returning all phone_numbers for each user.