I purchased an LG G2 on ebay to get me through until my iPhone 7 ships, had the same problem. I don't know if the USB debugging step is necessary, but here's what I did to get the app to recognize the phone:
1. Enable Developer Features (Settings > About Phone > Software Information > Tap Build Number like 5 times or something (it tells you how many after several taps) to enable developer features
2. Enable USB debugging (Settings > Developer options > USB debugging) - note that you cannot enable while the phone is connected to PC via USB. So unplug first then enable.
3. Start Software Upgrade Assistant software on PC.
4. Plug phone into PC and choose install/media sync mode.
5. Then go to phone and change the connection mode to internet > ethernet.
6. Update software started reading my phone status.
Unfortunately my device is 4.2.2 and software version "VS98008U" and says that it's up to date. I can't find any information about this software version anywhere, so I'm not sure what I got sold on ebay but it aint friendly. And all I want to do is upgrade to current Android version so I can install the latest ESPN Fantasy Sports app until my iPhone comes