Open BubbleUPnP settings -> Local and Cloud -> Enable Local Media Server -> Check all boxes except proxy -> Select Local storage and mount points -> Enable browse local storage (that will include internal storage, SD card, USB OTG)
Enable the phone's built-in Mobile Hotspot (I've used WiFi Tether Router for my rooted phone in the past but for some reason I couldn't get this to work using it)
Connect the Oculus Go to your phone's Mobile Hotspot WiFi
Open Skybox VR and select Network and then BubbleUPnP and you should be able to browse and play video content stored on your phone or attached USB drive using a USB OTG adapter.