Greetings Ciáran,
I'm building this new Joomla! 3.3.6 site using Enlighten: http://casite-642225.cloudaccess.net/
The facebook icon in the upper right displays well on the computer and the ipad. On an iphone it disappears. This is true on both the vertical and horizontal display. See attached screenshot.
Got CSS or an update to the template?
thanks,
Hope