Well if you want to change it you will need to change the plugin. The current version seem to be here: https://github.com/apache/cordova-plugin-inappbrowser
Just fork it and use it to build your app. You will need have a Mac computer to build for iOS though. You will find instructions on building applications on your computer on PhoneGap page (see also instructions for InAppBrowser, but note that you would have to pass an URL to plugin add command).
Note however that consistent experience on all systems is not really possible. For example Android already has a back button so it is not crucial to have it for users on Android. Experience in many cases should be consistent through all applications on the same system, not within a single application.