I tested in visual studio MyWebService.asmx and it works.
When I run it from the php page, I get exception in visual studio parameter not supplied. I guess there is something wrong with the php code.
<?php
$client = new SoapClient("http://localhost:1144/MyWebService.asmx?WSDL");
$arr = $client->PhpWebMethod($_GET['searchtxt']);
print_r($arr);
?>