Is there a way to download a PHP file without it being executed?

If the server is configured correctly, you cannot download a PHP file. It will be executed when called via the webserver. The only way to see what it does is to gain access to the server via SSH or FTP or some other method.

This is because PHP is a serverside language, all the actions are performed on the server, then the result is sent to your browser (which is clientside).

If you are afraid to mess with your system, you could use Virtualbox with an Ubuntu VM and open the page from there. If you take a snapshot of the VM after installing, and before doing dangerous things, you can later go back to that snapshot and undo anything the script could have done to the VM.

As others have said, the PHP file is executed server-side, unless the server is so badly set up that it will simply serve the source.

If you would like to examine what is sent to your client without the possibility of it doing anything untoward, use a text editor like Notepad to open the URL. That is, use File → Open but open the URL rather than a real file.

The server will interpret the request and send what it would normally send to a browser. Your text editor will receive it, but all a text editor can do is display if for editing. It will never get near a browser or other rendering engine to be executed.