To view software packages installed on you linux machine, use rpm -qa for RPM-based distro or dpkg --get-selections for Debian-based distro.
You can use the above commands in tandem with either less or grep for easy viewing of results.
e.g.
# dpkg --get-selections | grep php
libapache2-mod-php5 install
php5 install
php5-common install
php5-gd install
php5-mcrypt install
php5-mysql install
phpmyadmin install