require __DIR__ . '/vendor/autoload.php';
require_once 'libs/GPG.php';

$gpg = new GPG();

// create an instance of a GPG public key object based on ASCII key
$pub_key = new GPG_Public_Key($public_key_ascii);

// using the key, encrypt your plain text using the public key
$encrypted = $gpg->encrypt($pub_key,$plain_text_string);

echo $encrypted;