// 4. argument is the directory into which attachments are to be saved:
$mailbox = new PhpImap\Mailbox('{imap.gmail.com:993/imap/ssl}INBOX', 'some@gmail.com', '*********', __DIR__);

// Read all messaged into an array:
$mailsIds = $mailbox->searchMailbox('ALL');
if(!$mailsIds) {
	die('Mailbox is empty');
}

// Get the first message and save its attachment(s) to disk:
$mail = $mailbox->getMail($mailsIds[0]);

print_r($mail);
echo "\n\nAttachments:\n";
print_r($mail->getAttachments());