How do I install php mbstring extension in to Nginx Ubuntu

Question

I need this php extension in order to use one of my Magento extension. How do I install php mbstring extension to my Nginx Ubuntu 14.04?

Answer 1

EDIT: See Ajeets answer below for the correct solution

I don't think mbstring (like OpenSSL) depends on an extension, it should just be built into PHP. I'm running Raspbian and NginX and if I create a file with

<?php phpinfo() ?>

and look at it then I see: