This otherwise entirely useless app demonstrates how to connect to your Heroku PostgreSQL database in a PHP app.
Long story short, read your connection data from DATABASE_URL.
Every time you hard-code the connection info, god kills an octokitten.
Clone it, then create your Heroku app with:
$ heroku create --stack=cedar
Push your clone to Heroku:
$ git push heroku master
PHP apps don't get a database by default, so you have to add it manually:
$ heroku addons:add shared-database
Once that's done, you can visit your app with:
$ heroku open