I am not 100% sure, but, most likely it is:
- Apache (or Nginx or other) source
- PHP source
- PostgreSQL development (.h files)
- UNIXodbc or iODBC source
- Proper switches for building PHP (like '--with-xxxx'), too.
I know there is a paid support option for Vector Linux. Customers who would want to use it as application server platform will, most likely, need those features very much. With UNIXodbc or iODBC one could write PHP application which works with Oracle database on another machine or even with Microsoft SQL server on some Windows server.
It is not such a big deal, one could use proper pre-built Bitnami stack, which is also quick and easy to deploy. However, usually, those options exist in quite a few other distributions (Red Hat, OpenSUSE, Debian - those are ones I worked with).