Thanks for posting! Even though you have just un/re-installed, try the Admin Console > FileMaker Overview > Edit Server Deployment process again and then try the PHP test page. l know it seems a bit redundant, but a re-deploy usually helps for these types of cases. I'd also try the XSLT and IWP page just to narrow down this issue between PHP or the web server.
I'm sure your installation of FileMaker Server is not far off from my own:
-No other websites hosted on the web server
-Web publishing turned on with PHP, XML, XSLT, IWP checked (If you're not going to use XML, XSLT, or IWP it is not necessary to have them checked. It might be a good idea in this case, though for testing purposes. )
-FileMaker Server's PHP is installed (I'm not sure if you chose to keep your own PHP, but installing FileMaker's PHP might be worth a try for testing purposes)
-All of the FileMaker Server Advanced ports are open (Knowledge Base article 6427)
Hopefully, this gets us going in the right direction. Let me know how everything works out!
Check that on the sample database that PHP works, as this solution has the permissions set in the file. You do this by going to :
File > Manage > Accounts and privileges > Extended privileges > access via PHP web publishing
From what I just heard from Support, FM 12 Server Advanced no longer has a PHP Web Assistant available. Not avaiable on 12.. An't that a kick!