You may be getting an error because the function is actually scard_list_readers()
not SCardListReaders()
as the error shows in your post.
But before you can use most of the functions, you need to establish a context first.
Try:
$context = scard_establish_context();
$readers = scard_list_readers($context);
print_r($readers);
// then when you have your card reader's identity from $readers
$connection = scard_connect($context, 'YOUR CARD READER HERE');
$response = scard_transmit($connection, 'pdu string');