void debug_print_backtrace ( void );

<?php
   function one() {
      two();
   }

   function two() {
      three();
   }

   function three(){
      debug_print_backtrace();
   }
   one();
?>

#0  three() called at [/var/www/tutorialspoint/php/test.php:7]
#1  two() called at [/var/www/tutorialspoint/php/test.php:3]
#2  one() called at [/var/www/tutorialspoint/php/test.php:13]