In the AppBuilder simulator you can choose the device's platform and the platform's version. Unfortunately, there is no option to configure the resolution.
The simulator is not a fully functional emulator and has some limitations. For example, the screen resolution for a iPhone 5 in the simulator is predefined to 320 x 568 pixels and the original resolution on the device is 640 x 1136 pixels.
Also, you can use the "viewport" meta tag and place it in the index.html
file for additional configuration as explained in the official PhoneGap API documentation
Regarding the difference in the button sizes it may derive from the different screen resolutions, especially if the width of the button is defined in pixels which will prevent the button to retain its responsiveness in different screen sizes (e.g. will look smaller in higher resolution screens). For metric values such as lengths, widths, heights you may prefer to assign relative values
instead of absolute (like pixels).
Please, let us know if you have further questions.