Top smartphones today are very capable of capturing amazing quality video. On-board audio is always going to leave a whole lot to be desired though. The Balsang B6 microphone can help. It is a multi-directional shotgun microphone for smartphones and regular cameras. It comes with a front-rear directional mics and an omnidirectional mic. It also has ASMR and ambient noise cancellation modes.
The B6 microphone has forward/backward/bi-directional/360-degree modes. It has separate audio channels, so you can get creative with your sound. Expected to ship in April. You can find out more about it here.