Can't install Drush on FreeBSD
composer install will not install php; go ahead and follow the instructions in the Drush README for the composer install, and you should be fine.

Note also that Drush master (Drush 7) will soon require php 5.4, so you should use Drush 6 if you'd like to stick with php 5.3.

I don't have a FreeBSD system to try this on, but composer global require drush/drush:6.* works fine on my Linux box.  If you have problems with the composer install, you might want to try composer self-update, to insure that you have a recent version; I can't imagine why FreeBSD should be different than Linux when finding and installing Drush.