There are a number of ways to read debug data from the phone inside the bot.
The MarkSetBot team does it via USB and Android Device Log in Visual Studio with Xamarin installed. The phone must have USB debugging enabled.
Most of our calls are with Console.WriteLine and System.Diagnostics.Debug.WriteLine. That is read by filtering for Tag=mono-stdout
Some calls use Android.Util.Log.Info("MarkSetBot", pstrMessage). That is read by filtering for Tag=MarkSetBot (as of 8/2018, there are no active lines of code using this technique)