macportでphpをインストール

sudo port install php5 +apache2 +mysql5
sudo /opt/local/apache2/bin/apxs -a -e -n "php5" libphp5.so
sudo cp /opt/local/etc/php.ini-dist /opt/local/etc/php.ini

vi /opt/local/apache2/conf/httpd.conf

で、
Include conf/extras-conf/mod_php.conf

の最後の方に、
AddType application/x-httpd-php .php .phtml
AddType application/x-httpd-php-source .phps
を追加。

/opt/local/apache2/bin/apachectl restart

apacheを再起動