These are all behind the back cover, and are (from what I understand) pretty tiny, so I wouldn't imagine 'em to be all that convenient for toggling silent mode.

But yeah, my PinePhone's supposed to ship on the 25th and I expect I'll be missing that feature.

This button could easily be added by a third party protection case using the GPIO that is available on the pogopins at the back of the phone.

That's why people love OnePlus.