You and I have a similar setup, but both of mine are true laptops. I can verify your findings with the win 8.1 screen not sleeping. Have you gone into your screen setting and resaved the settings? I honestly cannot remember at this moment what I did to fix my issue like that.
Also, what is the phone software that you are using? And do you have any knowledge of how it works (ports, dependent services, etc.)? Even with rigorous testing there is no way to avoid potential conflict with ALL software.