You can run PHP as with any web-server, using the SPHP module for node.
It's compatible but not dependent on express.
It also supports websockets requests on the HTTP port.
Its biased for speed under small load, rather then saving resources.
To install in node:
npm install sphp
in you app:
var express = require('express');
var sphp = require('sphp');
var app = express();
var server = app.listen(8080);
app.use(sphp.express('public/'));
app.use(express.static('public/'));
For more information, look at https://github.com/paragi/sphp
I'm slightly biased too because I'm the author :)