No, otherwise, how would it know to turn on when you press the button.
The button you press is a "soft" switch, not an actual switch.
If the switch physically moves contacts that either remain closed in one position, or open in the other, then it is "off"
Otherwise it is just mostly off, and an iphone is less off than most.
A very short google will explain most of it. When you see bad guys in movies remove the batteries from their phones, they are not just making it up. They really have to do it.