To display or show what version of php you have installed on your pc, server, computer, laptop or any device where you have a unix operating system.
Execute this command:
php -v after you have send this command, you should see something like this:
[root@host ~]# php -v
PHP 5.1.6 (cgi) (built: Jan 23 2009 22:02:39)
Copyright (c) 1997-2006 The PHP Group
Zend Engine v2.1.0, Copyright (c) 1998-2006 Zend Technologies
If server response is not something like the above, then it means that you don't have php installed in your server.