right now I am fetching some values like system name, up-time of the system
Thats fine. SNMP is a system management tool. PHP can do similar things
But you are talking about getting information from a client machine.
Entirely different. May I suggest you read about the Server-Client relationship and how that fits into the the OSI model.
Then you will know what Dormilich means by
PHP has nothing to do with the client machine. those status values you need to fetch by a client side application
So it is a case of a client application passing the info via the system to a server side application.
An interesting project.