So you've built a webserver and the question remains:
How do I add PHP functionality to it?

To tackle this problem first you need to understand the core working of PHP.
PHP isn't a server application on itself, it's just a processing application, intended as a server plug-in.
Servers applications only have the task of interpreting the requests and sending a response back.
So if you put a PHP-file in php.exe it processes the file and gives plain HTML as output. And the server application sends it as a response to the request.

Knowing this it's just finding a way of capturing the output and selecting the correct parameters.
Puzzling around I've built the following function which will allow you to set the parameters and capture the output of php.exe.
Code:
Public Function ProcessPHP(ByVal FilePath As String, Optional ByVal phpPath As String = "C:\XAMPP\php\php-win.exe", Optional ByVal Args As String = "-f") As String

    'Using reference to: Windows Script Host Object Model
    '                    "System32\wshom.ocx"
    
    '/// Declare Shell Objects
    Dim Shell As New WshShell
    Dim retObj As WshExec
    Dim retStr As TextStream
    
    '/// Declare Basic Variables
    Dim cCommand As String
    Dim q As String
    
    '/// q is for quoting the filepath correctly in the command
    q = """"
    
    '/// Put together the command
    cCommand = phpPath & " " & Args & " " & q & FilePath & q
    
    '/// Execute command
    Set retObj = Shell.Exec(cCommand)
    
    '/// Put return value in textstream and make a string value out of it
    Set retStr = retObj.StdOut
    ProcessPHP = retStr.ReadAll

End Function
Usages as follows:
Code:
[ResponseHTML] = ProcessPHP([PHP file path], [php-win.exe location])
Don't forget to set reference to the "Windows Script Host Object Model".

TheBigB.