The article below shows the different way of embedding advertisements in phpBB3:

http://www.phpbb.com/kb/article/advertisements-in-phpbb3/

However, if you tried editing the template files and the advertisements are not showing up, you will have to clear phpBB3 cache, not the browser cache that we normally clear.

By default, phpBB3 keep a cache of the template for faster generation time and reduce server load. So after editing the template files, go to administration control panel.

Click on Styles tab, follow by Templates under Style components on the left-hand menu. Then, click on cache, marked all template files and delete.

An example below:

Refresh your browser on the phpBB3 forum and the advertisements should appear as on how you edit your template files!

* Sorry for the above unclear image, the actual size just doesn’t fit my template.