Vue.js – PHP -> How to API call?

My company created callcentre in PHP few years ago and now they need to upgrade it.
I created Vue.js callcentre frontend application and now I need to start connecting it with old PHP. Problem is that I never used PHP before. I mounted my vue app to receive server side events from backend. So whenever someone calls operator from callcentre, it will send event to my vue app. So I can show answer call button but I need to create functionality for it, whenever operator clicks it will answer that call. Same for hang up.
So I created two methods in vue and using axios I am sending post request to php backend.

Code below.

   answerCall(){
      let channelId;
      for(let i in this.getChannels){
          channelId = i
      }
      console.log(channelId);
      axios.post("/hzs/answer", channelId)
          .then(response => console.warn(response))
          .catch(error => {
              this.error = error.message;
              console.log(error);
          });
  },
  hangUpCall(){
      let channelId;
      for(let i in this.getChannels){
          channelId = i
      }
      console.log(channelId);
      axios.post("/hzs/hangup", channelId)
          .then(response => console.warn(response))
          .catch(error => {
              this.error = error.message;
              console.log(error);
          });
     },

As you can see, I am sending channelId. That is just long random string which tells php who is calling. I am recieving it from event.

My problem is with PHP, because I don’t know how to use it correctly. This is what I have for answering call. It is created by me, before it was in huge switch case so I just copied it and pasted in new file, where I send http request.

<?php
  require_once('/var/www/modules/callcentre/functions.inc.php');
  require_once('/var/www/modules/callcentre/constants.inc.php');
  
  if(!authorized('callcentre_admin') && !authorized('callcentre_supervizor') && !authorized('callcentre_agent'))
         return false;
  
  function call_answer()
  {       
        $channelid = $arg;
        if (!preg_match('/^[0-9a-z/.-]+$/Di', $channelid))
               $channelid='XXX';
        ccSendToDaemon('answer ' . $channelid . ' ' . $uid);
        break;
 }
 
 header('Content-Type: application/json');
 echo json_encode($defaults);
 
 ?>

How can I achieve that after sending POST request to php I can trigger “ccSendToDaemon”?

Hope someone will be able to help me. Thank you for reply.