While implementing a NetGet handler in PHP, I ended up with this basic IfbyphoneNetGetReply class as a way to keep my code clean.  Code:

http://gist.github.com/279469

Sample use (live): http://gist.github.com/279481

The URLs have more, but here's a sample:

$ibp = new IfbyphoneNetGetAction('survo', array('id' => 1234, 'p_t' => '42'));
$ibp->set_user_parameters(array('name' => 'sergey'));
print($ibp->asXML());

Save ifbyphone_netget_reply.php in the same directory as your script, then require() it like the sample does.  Make sure PHP XML support is enabled (often the 'php-xml' OS package; check phpinfo() or "php -m").

Troy