PHP / MySQL on Clean Install

Assuming php5_module is eanbled in the module list, you'll need to get php.ini created and configured for local requirements from the /etc/php.ini.default default using nano or vim or such, and you need to enable CGI execution for the particular web site in the options tab and add (usually) index.php or such into the list of files in the default list in the general tab of the web site. You might want server side includes and you probably do not want WebDAV and folder listings.

Quick write-ups I did a while back here is how to enable php on OS X Server and FWIW, here is how to enable php on OS X client. The latter has some more details on working with the php.ini file.

And FWIW and solely to confirm your DNS services are correct — mentioned only because DNS is fundamental to the whole configuration of OS X Server, and getting DNS wrong tends to cause cascading failures in other services and difficulties — launch Terminal.app and issue the following non-distructive diagnostic command:

sudo changeip -checkhostname

After some chatter about the local host, that'll then (usually) tell you if DNS is correct or if it needs changes.

I don't use phpmyadmin. (If you do choose to install and use that tool, do not allow remote access into that tool on your web server.) For these sorts of tasks, I'll generally use the command line, and the Sequel Pro tool can also work nicely for some of these tasks. Here is some set-up information for Sequel Pro on OS X Server 10.6.