I found that the magnetic button will work if you turn the phone upside down (power and volume buttons down). This will render the startup menu and some of the apps upside down. I wrote to Unofficial Cardboard about this, and they are sending me a stronger magnet to try (in its original position on the left). Alternatively, you can reconstruct the box with the magnet on the right side, so you can mount the phone properly, right side up.

dave