The PHP Mysql port is a little bit of a pain. By default Macports doesn't set a default mysql sock. That leads to an error something like this:
SQLSTATE[HY000] [2002] No such file or directory.
You fix it by just appending the sock file for the mysql version you're using into the PHP mysql.ini file. I use mysql55 so to fix PHP I do this
echo 'pdo_mysql.default_socket=/opt/local/var/run/mysql55/mysqld.sock' | sudo tee /opt/local/var/db/mysql.ini