How to access packages in vendor directory

Calling any package from the vendor directory structure within any CakePHP controller works, as the composer set up everything correctly. For example this MCVE from https://github.com/giggsey/libphonenumber-for-php#quick-examples

$swissNumberStr = "044 668 18 00";
$phoneUtil = libphonenumberPhoneNumberUtil::getInstance();
try {
    $swissNumberProto = $phoneUtil->parse($swissNumberStr, "CH");
    var_dump($swissNumberProto);
} catch (libphonenumberNumberParseException $e) {
    var_dump($e);
}

When I run the equal code directly in webroot/sample.php so it fails :

Got error ‘PHP message: PHP Fatal error: Uncaught Error: Class ‘libphonenumberPhoneNumberUtil’ not found in …sample.php

My question:

What do I have to do outside the CakePHP world so I can use the packages in the vendor directory structure?

Answer

I was now looking around and I saw in the vendor directory the file autoload.php and I gave it a try.

The solution is:

Outside the CakePHP world I have only to include this autoload.php:

include( __DIR__ . '/../vendor/autoload.php');

Then all packages in the vendor directory became available.