Ios client application needs to add a new client to a twilio conference call dynamically

Question

I'm facing a problem with add new member's to a conference call. I have a php server, and ios app as a client. And a twilio system of agents and clients. Once an agent and client are connected into a conference call, they talk and everything is ok here. But, there's an option where a client by using his ios app wants to add a new member to the conference call. The new member can be someone a client knows and when he presses in the app a button(+) while in conference with agent, i must catch that phone number on the server route /addNewMember and then i can do this

function addNewMember($addNewMembNumber){
   ...
   $call = $client->account->calls->create(
      $twilioNumber,
      $addNewMembNumber,
      "SOME TWIML CODE", 
      array()
   );

}

I can call the client(member) and add him to the conference call. But how can I do this in ios app. So my question is how can I pass the phone number to my server route while in a call with agent?