Currently on Android, the Voice chat is considered (by the phone) to be an actual call. i.e. The 'call' volume slider controls the volume.
Most phones use mono and filtered audio (Certain frequency ranges are cut for better clarity for voice; Bass is cut and above 10k Hz is also cut)
But the main problem is, when joining a voice chat, any other sound is also attenuated to the above conditions making it nearly impossible to play game or audio.
It would be really nice if there was an option to treat it as media output thus allowing us to use discord for playing games on phone.
Side note: PUBG does this nicely.