What you are asking for would be a major security problem. It is not possible to ask for the php-code instead of the result of the php script execution. Well, not exactly - it is up to the Server hosting that php script what it does with it. If there was no php extension installed on the server it would return the php code or the file as whole.
But to help with your request: You should ask the server administrator / website owner if the code is available somewhere and if so what the url is. I believe there is a php extension that allows files to be looked at with colors, text indent and everything - but i think it is disabled by default (or you need to rename your php file to something else)