result.txt

$ ACCESS_TOKEN=111111 php index.php 
array(2) {
  'usedBytes' =>
  string(8) "82656436"
  'availableBytes' =>
  string(11) "10654761804"
}

yandex-disk-test.php

<?php

require './vendor/autoload.php';

use Yandex\Disk\DiskClient;
$accessToken = getenv('ACCESS_TOKEN');

$diskClient = new DiskClient($accessToken);
$diskClient->setServiceScheme(DiskClient::HTTPS_SCHEME);

$result = $diskClient->diskSpaceInfo();

var_dump($result);