They are plastic buttons that hit a pad. Can you turn "off" your laptop keyboard keys "sound"?
On most cell phones, the keys are “virtual” (i.e. they are nothing more than a particular location on a touch screen).
The “click” sound is entirely optional and can be turned on and off. Even on the older phones which have an actual keyboard, the keys are constructed differently from those on a computer keyboard, and most are not inherently noisy.
I think this is what “a fool in paradise” was referring to.