Almost entirely sourced from http://stackoverflow.com/questions/6588174/enabling-postgresql-support-in-php-on-mac-os-x but I'm keeping a copy for myself along with my tweaks.
OS X 10.10 comes with PHP 5.5.20 which you'll need to grab from http://php.net/get/php-5.5.20.tar.bz2/from/a/mirror
I'm running my copy of PostreSQL from Postgres.app so get a copy and install to your Applications folder.
cd ~/Downloads tar -jxvf php-5.5.20.tar.bz2 sudo mkdir -p /usr/include sudo mv php-5.5.20 /usr/include/php cd /usr/include/php ./configure --without-iconv cd ext/pdo_pgsql brew install autoconf phpize ./configure --with-pdo-pgsql=/Applications/Postgres.app/Contents/Versions/9.4/ make sudo cp pdo_pgsql.so /usr/lib/php/extensions/no-debug-non-zts-20121212
In checking php | grep ini I spotted that the base install was expecting additional configuration files within /Library/Server/Web/Config/php. That didn't exist so I created it along with in ini file containing extension=pdo_pgsql.so
sudo mkdir /Library/Server/Web/Config/php
With that done php -m should now list pdo_pgsql as an included module