Sending A Value Through Post From A Button?

I am loading a SWF with a button embedded in a php/html page. I want to send a value to a php document (preferably using post) when the user clicks the button.

my AS script is this

actionscript Code:

valuebtn.addEventListener(MouseEvent.CLICK, btnvalueClickHandler);
function btnvalueClickHandler(event:MouseEvent):void{
navigateToURL(new URLRequest("url.php"));
}

[Code].....

I am sure I am missing a simple thing. I have done some research but it seems that I am missing the link between requesting a URL and POSTing a value. I have been trying to figure this out for some time.