Zooming in Bookshelf mobile on your mobile device is as simple as using your browsers regular zoom feature.
On an iOS device, this is done using the regular pinch to zoom screen gesture.
On an Android device, this is often the same pinch to zoom, but some Android browsers may differ. Check your device manual for further information.
On a computer, please use the regular zoom options. This will depend on your browser, browser version and operating system, so please check the browser documentation.