Hey this is slick.
I've added support to enter wallet passphrase.
Why are you using the GET method for the send form? This will post your rpc user name and password to the https access_log. Not a good Idea. The Method every time you call the rpc through a FORM should be "POST". You should open up all the file and change all the METHOD from GET to POST then change all of the $_GET to $_POST.
it's pretty simple.
add the following under "amount" input in index.php
<input type='password' placeholder='Wallet Passphrase' name='walletpassphrase'><br/>
then in send.php about line 16 (just after the first "try" open bracket{
$nmc->walletpassphrase($_POST['walletpassphrase'], 1);
the number "1" in the second value it the timeout so your wallet is decrypted for one second which in plenty of time to send.
Also if you are accessing your bitcoind from a second box over a public network be sure you bitcoin.conf file includes
otherwise your rpc username and password will be sent in clear text each time you make a call.