将server.js中的数据发送到要处理的PHP文件

When I submit a form from my client side the relevant data from the form is showing up as req.body on my server. I want to pass that data to a PHP file to process. I don't know how to run the PHP file and pass it an argument from inside the js file.

app.post('/contactengine.php' ,function ( req, res ){
  data = req.body
  //the data is showing up here correctly.
  //I would like to take data and get it processed by contactengine.php can anyone help?  I dont know how to run the PHP file and pass it an argument.
});

</div>