Question

I have this php function inside a class the returns json data

function getPhotoDetails( $photoId ) {
   $url = $this::APP_URL . 'media/' . $photoId . $this::APP_ID;
   return $this->connectToApi($url);
}

and this ajax request

function getPhotoDetails( photoId ) {
    $.ajax({
        type: "GET",
        cache: false,
        url: 'index.php',
        success: function (data) {
               console.log(data);
        }
    });
}

The question is how I can call the php function to get the json data.

Solution:
A big thanks to all of you guys and thanks to Poonam

The right code

PHP:
I created a new object instance in php file

$photoDetail = new MyClass;
if(isset($_REQUEST['image_id'])){
  $id = $_REQUEST['image_id'];
  echo (($photoDetail->getPhotoDetails($id)));
}

JavaScript

function getPhotoDetails( photoId ) {

    $.ajax({
        type: "GET",
        cache: false,
        url: './instagram.php?image_id=' + photoId,
        success: function (data) {
            var data = $.parseJSON(data);
            console.log(data);
        }

    });
}

Answer 1

Try with setting some parameter to identify that details needs to send for e.g assuming photoid params needed for function

function getPhotoDetails( photoId ) {
    $.ajax({
        type: "GET",
        cache: false,
        url: 'index.php?sendPhoto=1&photoid=23',
        success: function (data) {
               console.log(data);
        }

    });
}

and then on index.php check (You can make check for photoid whatever you need as per requirement)

if(isset($_REQUEST['sendPhoto'])){
      $id = $_REQUEST['photoid'];
      return getPhotoDetails($id);
}