You would find a reference to the mime types file in the Apache's config file. The line may read something like TypesConfig /etc/mime.types
the mime.types file is normally readable by all users.
And it looks like this:
application/msword doc
application/news-message-id
application/news-transmission
application/octet-stream bin dms lha lzh exe class
application/oda oda
application/pdf pdf
application/pgp-encrypted
application/pgp-keys
So...this list can be huge. A better idea would be to know the content types that you would like PHP to output and then code your PHP scripts accordingly, rather than parsing the entire mime.types file
good luck!