Depending on your device's screen resolution the Guitar Tunes layout will automatically switch to the best layout based on the screen's total space available. It is more common for devices that fall in-between standard phone or tablet layouts to default down to the phone layout. Example, phablets often use the Guitar Tunes phone layout becuase while it is beigger than a phone it is not quite as big as a true tablet.
If your phone or tablet allows for the changing of the screen resolution, changing it to be higher can make the layout automatically switch the app to being viewed as a tablet and lowering it can change it to being viewed as a phone.
It will depend on your Android OS version and the device manufacture's variation choices for Android if changing the screen resolution is an available option in the device's settings.