返回PHP代码,而不是显示正确的输出

Good evening to everyone. Let's go straight to the point. I have a weird client/server configuration, which I have to replicate: I have an IIS machine (v. 8.5) that is used to run old ASP classic code, and a Linux machine running Apache2, PHP, PostgreSQL. The IIS machine is the one directly accessible from the web by end users. It is used to show them the output provided by the Linux server which is the real content provider, but it is physically located on an internal network. I know, it's weird, but I had no part in this ;). Anyway I should replicate this exact situation on a local machine, and I'm simulating this, using an Ubuntu 15.04 netinst VM on a Windows10 machine. Both the default Apache and php-info page are correctly displayed from the Windows browser. The asp pages on the IIS are more or less all like this:

Server.ScriptTimeout = 360
Select Case Request.ServerVariables("REQUEST_METHOD")
Case "GET"  strRequest = Request.QueryString
Case "POST" strRequest = Request.Form
End Select
strURL = "http://LinuxServer/corrispondingDestinationPage.php?" & strRequest
Dim objHTTP
Set objHTTP = Server.CreateObject("MSXML2.ServerXMLHTTP")
objHTTP.open "GET", strURL, false
objHTTP.send ""
Response.ContentType = objHTTP.getResponseHeader("content-type")
Response.BinaryWrite objHTTP.responseBody
Set objHTTP = Nothing

They should just display the output provided by their php counterparts on the Linux server (mostly user tables and stuff like that). The thing is that on my local reproduction of the system, instead of getting the output, I'm receiving directly the raw php code from my VM. I have previous experience in configuring just standard LAMP servers, so probably I'm missing something on the configuration of both machines, the IIS and the Linux VM. Do I need to install some specific functionalities on IIS, or some specific modules on the Linux machine? Thank you very much in advance for your time. Best GLB

First edit: I'm just making some tries in order to understand which could be the problem. While experimenting, I've discovered that if I access the php pages directly in the VM, the browser displays part of the php script of the page. If I access the system as it should be (from the IIS index page), instead, I fill a debug variable in order to understand what is going on. In this way the variable fills with the whole raw php code of the page, which is called from the asp page. In every case it seems that the php processor is not functioning as it should.