Having a great camera probably is included in the top three of what consumers look for in a smartphone. From 4K video capture, to ridiculous slow-motion, there’s no denying the swarm of features that our smartphone cameras can tap into. Video recording can be a drag if you have a great camera but your audio is not as good.
One of the best external mic in the market is the Purple Panda Lavalier Lapel Microphone Kit. It connects via the headphone jack on your smartphone, requiring very little setup to get running. This is the cheapest, arguably most effective way of improving your audio quality.
Check out the complete list here: https://www.phonearena.com/news/5-Best-External-Microphones-for-Smartphones_id100259