Will check to see if the call was made internally or externally.

internalCall.php

<?php

namespace foo\bar\baz;

use ReflectionClass;
use ReflectionMethod;
use Exception;

class foo {

	public function internalCall($class, $exception) {
		$trace = $exception->getTrace();
		return count($trace) > 1 && isset($trace[1]['class']) && $trace[1]['class'] === $class;
	}

	public function bar() {
		return $this->baz();
	}

	public function baz() {
		return $this->internalCall(__CLASS__, new Exception);
	}

}

$foo = new foo();

var_dump($foo->bar()); // true
var_dump($foo->baz()); // false