The subject should be what is inputted into the subject text box. You will get the no body error if nothing is entered, I think.
This isn't the most foolproof method btw, the mySQL method is a lot better IMO. But that takes lots more coding and stuff.
Also, for a better method, add this to the top of that php on contact2.php:
$name = htmlentities($_POST['name']);
$email = htmlentities($_POST['email']);
$phone = htmlentities($_POST['phone]);
$message = htmlentities($_POST['message']);
$mailsubj = "$subject\n";
$mailsubj = "From: $name\n";