$ sudo port install php5-xdebug
Password:
--->  Fetching php5-xdebug
--->  Attempting to fetch xdebug-2.0.3.tgz from http://www.xdebug.org/files/
--->  Verifying checksum(s) for php5-xdebug
--->  Extracting php5-xdebug
--->  Configuring php5-xdebug
--->  Building php5-xdebug with target all
--->  Staging php5-xdebug into destroot
--->  Installing php5-xdebug 2.0.3_0
    ***************************************************************************
    * To enable the xdebug extension in php, add or edit the following
    * lines in /opt/local/etc/php.ini:
    *
    * zend_extension="/opt/local/lib/php/extensions/no-debug-non-zts-20060613/xdebug.so"
    *
    * Once the extension is installed, you can get a list of the available
    * configuration settings with the following command:
    *
    * % php --ri xdebug
    *
    * For more information and details about configuration settings, see
    * http://www.xdebug.org/docs/
    ***************************************************************************
--->  Activating php5-xdebug 2.0.3_0
--->  Cleaning php5-xdebug

php.iniに以下を追加。

zend_extension="/opt/local/lib/php/extensions/no-debug-non-zts-20060613/xdebug.so"