Maybe this post could help you: http://billpatrianakos.me/blog/2014/04/25/phonegap-for-ios-the-definitive-guide-to-using-custom-fonts/
A few extra questions, are you testing on a device that is < iOS 10? Is the phone connected to the internet? Have you checked the console to see if the browser shows an error?
Furthermore you could try and include a .ttf font as some of the sources on the internet suggest that .woff2 fonts are incompatible with iOS. (however these are quite old sources).