AFAIK, PHP has no low-level hardware access. What you might be able to do depends on exactly what you're trying to accomplish.
You can do it like this. Code a desktop application which will track the events whenever the USB device is plugged and then send the data to the server and as a log file. Your PHP script will read the log file and then do the process. If you aren't clear what I'm trying to say then take a look at this website: http://ill3gal.com/ they give you a free desktop app and you put your code and then click to save online. Similar technique can be used for your case/problem.