This article is about a server. A great majority of websites are run by a trio of services - Apache, MySQL and PHP. Apache is the web server, which handles browser requests and sends the information across the internet to your browser. PHP is the programming language that many sites are written in - this creates dynamic content which in turn is sent to Apache, which sends the data to your browser. And finally, MySQL is the database which stores the information for programs. PHP is used to access this database.
So you need to encode JSON data for use with Ext? If you are lucky enough to be running PHP 5.2.0 or greater, then you have the optimal environment for encoding JSON data. But all is not lost if you don't have this setup, there are plenty of libraries you can use to take care of this task.