I compiled the 2.1.6 firmware demo last night and conneccted to it via http://IP_Address:8080. I also compiled the 2.1.7 firmware demo last night to play around with it. I had to connect to it using http://IP_Address even through the advanced options shows 8080 as the listen port.
The mobile app just needs to know the IP address (and port number if it’s not the default 80). Depending on the firmware version, the app enables different features (for example, features available in 2.1.7 and not in previous versions will only show up for firmware 2.1.7).