Your iPhone is capable of capturing great video but you will need an external microphone to take your audio captures to the next level. The Saramonic Blink 500 B4 Lavalier Mic can help. Designed for journalists, vloggers, and YouTubers, this kit has 2 omnidirectional lava mics and a 2-channel receiver with a Lightning interface.
Thanks to this microphone system, you can record two subjects on your iPhone or iPad. It has a 24-bit / 48 kHz resolution. The transmitter lasts up to 5 hours on battery for long shoots. You can use up to two transmitters with each receiver (total of 18 systems in the same environment).