GPIO Button Adapter
The GPIO Button Adapter is a clean and easy way to add buttons to a Pi Zero alongside a pHAT (or HAT).
When a button is pressed, the GPIO gets connected to ground. The internal pull-up resistors on the Pi should be used so that the GPIO are HIGH when idle, LOW when the button is pressed.
Because the board is only 1mm thick, you can solder the GPIO adapter directly to the Pi header, leaving enough depth on the header pins to properly fit a pHAT on top of it, with good electrical connections.