Totally awesome guide is at http://rasberrypibeginnersguide.tumblr.com/post/27283563130/nginx-php5-on-raspberry-pi-debian-wheezy
But instead using provided silex site config file, you should configure root folder of web server to serve php scripts. To do so please rm symlink to
silex file and edit
/etc/nginx/sites-available/default
Set root folder to /var/www
# root /usr/share/nginx/www;
root /var/www;