The onSubmit event handler didn't work.
I think this handler executes the JavaScript command before the action of the form (in this case the execution of the phpfile1.php).
It's like when we validate the contents of various input fields before executing the action of the form, the validation triggers with the onSubmit event handler.
I don't know if there is a way to start the execution of the php file onSubmit or onMouseDown. Then I could stop it onMouseUp.
(Or start onKeyDown and stop onKeyUp respactively).
I'll try on that direction.
Thaks for your time.