There are several ways how you can check the version of PHP running on your web server.
If you already are comfortable in writing a PHP file, you can simply create a php file with this content in it:
Say you named it phpinfo.php, you would just need to point your browser to:
You will see a long page diplaying the version of your PHP that you are running, the different modules that were built when the PHP was compiled, etc.
The other way check the version of your PHP is by going to Shell and type:
It will immediately tell you what version of PHP that is on the server.