-
I'd go with a USB mic. Not sure if they work in all apps but this is meant to be a decent one for recording https://play.google.com/store/apps/details?id=com.extreamsd.usbaudiorecorderpro&hl=en
-
Bluetooth mic.
Actually.. scratch that, there are none that are decent even though the bandwidth would be fine.
I'd probably go for a basic condensor lavalier and cable it up: http://www.shure.com/americas/products/microphones/motiv/mvl-omnidirectional-condenser-lavalier-microphone
Can anyone give any advice on using an external microphone with a nexus 6p? I play in a few bands and it'd be nice to make dodgy practice demos a bit less dodgy. If there's some way of using an external mic I think it'd probably be a huge improvement on wrapping a phone in a jumper.