PHP files need to be executed (like an application on your computer). The file is read and then the output is returned to your web browser. Usually that output is in the form of HTML but it could also be JSON, or an Image, or a PDF or CSV file, etc. In order for your web server to know what to do with PHP files you will need to install a module to interpret those files. Most shared hosting plans already have this taken care of for you. Your web host (webatu) already provides support for PHP but you will need to navigate to that PHP file in your browser's address bar. You cannot simply double click on the PHP file.
Another option which is much simpler would be to use an iFrame of another blog (like blogger, tumblr...) inside of your HTML page. This approach has several downsides (bad for SEO, screws up the browser back button and navigation, etc.) but is much easier to get up and running.