The “Home Button” on an iPhone isn’t actually a button. It’s just a piece of glass over a sensor. The sensor detects a “press” and the phone uses the haptic vibration function in a specific pattern to simulate a clicking sensation.
You can test this by turning the complete phone off (not just in sleep mode). Hold the power button until it says to slide to power down, then do that. Once the phone is completely off, press the home button and notice that there is no click, there isn’t even any movement as you press it, it’s just a solid piece of glass. Even easier is to press the home button with your finger covered in some fabric, like the hem of your shirt, again, nothing will happen, the “button” will have no travel as you press it and there will be no click, you’re just pressing on a piece of solid glass, the clicking is just an illusion.
It’s interesting that it’s possible to simulate clicking with the right pattern of vibrations. Game developers can use controller vibration functions to do more than just simulate getting hit.