I'm developing my templates for Joomla and I'm needing to get the URL of the 'Featured Image' of an article. Is there a special Joomla PHP call to get this as a variable?
AFAIK, You cannot get this directly in the template's index.php file, but you can access it using the template's overrides. So start by creating a HTML folder within your template, then within that folder copy the folders you wish to override.
So for the image url, copy the following file components/com_content/views/article/tmpl/default.php to templates/yourtemplatename/html/com_content/article/default.php and then within that file you can access use / access the image url.