How Power BI Server (V 14.0.600.301) on Windows Server 2012 R2 for inernet access ?

As long as you Mobile device can access resources within your Intranet there isn't anything special you need to do to connect to a report server. For the mobile app you just need to register the server using the URL and same for the browser you just need to enter the same URL. If you can't access resources within your intranet you'll need to check with you IT department to figure out what you need to do to get access.