Is there a way to use jQuery to lock a device in portrait mode?

I am using PhoneGap and testing on an iPhone 6. I have tried editing "config.xml" to have the following:

1.  <preference name="orientation" value="portrait"/>

But when I load the app on my phone (via PhoneGap) it still changes to landscape. I'm keen to prevent this as it throws my layout into disarray.

Thanks

Wayne