Update: This has already been implemented see the API Blueprint Specification.
Original answer:
TL;DR: Not supported, planned
As far as I can tell, although you can provide multiple responses, you can only do so if the response code or content type differ.
Your findings are indeed correct. There is currently no way to do this. I was pondering this idea a lot lately. The solutions seems to be lift this restriction and implement the implicit transaction examples – Automatic request response pairing.
Note that in your case this seems to me like two different transaction examples based on the request
(pseudocode):
Example 1:
- Request With Phone Number
- Response With Phone Number 200 (application/json)
Example 2:
- Request Default
- Response Default 200 (application/json)
Assuming include=telephone
is a URI query parameter this planned feature will need next to the automatic pairing also the syntax for describing URI parameters values.