Hey John,
If I am understanding you correctly, you are using the Google Chrome browser on a desktop/laptop to view a NetTalk web app. Then resizing Crome's browser window to imitate a mobile device.
This tactic will not trigger the automatic change between desktop to mobile mode. For example, if I am using a laptop with a 15 inch screen and I open a Chrome browser on it. Then resize the Chrome window to resemble a 4 inch screen. The actual screen size is still 15 inches. What Bruce does (PLEASE correct me if I'm wrong Bruce), is set the NetTalk web app to mobile mode, then resize the Chrome browse to resemble a small screen.
This is what I do, I have my handy dandy Android phone next to me and point it's browser to the appropriate IP address. I can then look at my web app in mobile mode on a real device.
Don