While PHP is not one of the standard runtimes provided in the Bluemix catalog, the sample code in this git repo (
https://hub.jazz.net/git/u27275/blm-hello-world-php/) will show you how to bring your own buildpack, and this buildpack will allow you to have PHP code running in Bluemix that also can talk to a MySQL database running in Bluemix.
Among the files there is a PDF providing detailed instructions on how to set things up in IBM Bluemix.
P.S. This is sample code. See the licence file in the repo for more details.