Two months ago I was looking for a way to let apache serve python scripts as plain text. Today I had the same problem with php files. Here is my solution.
What you need is a
.htaccess file in the same directory as the files you want to serve, with the following directive in it:
AddType text/plain .php
Be carefull: within the directory, anybody will be able to look the source code of all files with .php extension.