Hi ! 🙂 Once you have enabled ADB on Linux VM, then check whether adb detects your mobile device. If not then you have to explicitly change settings through Oracle VM Manager. I have state here the steps to proceed.
First plug your device to the machine. Then;
Goto -> Oracle VM VirtualBox Manager–>Select UbuntuVM (Your Linux VM) –> Settings—>USB –> Select Add filters from device at the left side panel –> Select your device from the suggestions.
Restart your Linux VM (UbuntuVM)
This will install required device drivers and enable the connection between your mobile device and Linux VM.
Open a new terminal -> Execute adb devices command
This result on terminal will show your mobile device as a connected android device.