You could either send information about which function you would like to call on the url parameter ($_GET)
$.ajax('myserver.php?function=ajaxRetrieveData');
or adding into data object ($_GET or $_POST) :
$.ajax({
type: "POST",
url: "myserver.php",
data: { function: 'ajaxRetrieveData' }
});
and then using a router to find the function
myserver.php
$function = $_POST['function'];
$object->$function();
Please, do not use this code without properly validation.