Hai
In a sense, yes.
You can use AJAX (combination of JavaScript and server-side pages) to send/receive data from a web page and the server. So, you could use any JavaScript trigger to call a function that will "grab" a value from the form, submit it to a PHP page (transparent to the user) and return back the results to the JavaScript which can act upon it further.
One common use for this would be if you have dependant select lists. For example, if you want the user to select a region and then select an office in that region, you would want the "office" field to dynamically change when the region is selected. For a small list I would do this all in JS, but for large or complex lists you could use AJAX. When the user changes the region, JS is used to send the selected region to a PHP page which returns the list of offices. The JS then uses that list to repopulate the "offices" list.
There are many AJAX turorials available on the web.