While having a Bluetooth connection active between my kde desktop and my phone (note 4) and playing media on my phone (vlc and Netflix both tried) whether a file is being transfered or not, the sound plays on the laptop speakers instead of the phone for some reason
Your phone is playing it's sound output to your computer because you probably have pulseaudio-bluetooth installed or configured it to do so. If you don't want that, you can uninstall this package or simply disconnect your phone from your desktop. It is not a bug in bluedevil hovever.