I used to be able to mount the android phone, however after installing ADB, I can't seem to get the device mounted.
Some troubleshooting methods I tried:
Solved: The problem was from using the MTP option in the android phone (note that I'm running Android 5.0).
Swipe down the notification widget from the top of your screen --> Tap for more USB options --> Select PTP
Now adb devices is showing something like:
List of devices attached LGD855a0000099 device