I have an application that requires PHP 5.3. Is it possible to specify what version of PHP to run?
It's not currently possible to specify the version of PHP in the PHP and PHP-Worker services. The current version (as of this posting) is 5.4.6-2~lucid+1
If you need a specific version of PHP, it may be possible to use a custom recipe to download and install the specific version your looking for. The following project is an example of such a custom service.