Here's what Brivvio founder, Adrian, has to share about using microphones with Brivvio...
For most casual off the cuff videos, where you are holding your phone while recording, the built in microphones in the phone do just fine, as long as there's not too much background noise.
If you're going to be holding the phone and there is background noise, or you just want to improve the audio quality further, then using a lapel microphone can reduce the amount of background noise, because they are designed to only pick up audio within a small area.
If you're planning on being a bit further from your phone, or filming someone else standing further from the phone, then there are 2 ways to go - lapel microphones (attached to the speaker), or direction microphones, attached to the phone.
Lapel microphones (wired & wireless)
There are wireless and wired options, and some kits have the capability to have more than one person mic'd up at the same time (i.e. for interviews). Lapel microphones only pick up sound from a small area and need to be attached to the speaker. For lapel microphones I recommend the following options:
Directional microphones need to be pointed directly at the subject to work best. You'll also need an adaptor kit to clip the directional microphone onto your phone.
For directional microphones, I'd go with one of these.
If a person will be holding the phone while filming, I recommend the following directional microphone. It might look compact and handy, but because it is directly attached to the phone without anything to eliminate vibrations, every tiny movement of the hand holding the phone transmits into the microphone and can be heard very loud.
So I recommend avoiding directional microphones like this: https://www.rode.com/microphones/videomicmel
TRS vs TRRS sockets
If you are using a phone with a 3.5mm socket (not a lightning adaptor), you'll also need to bear in mind that all mobile phone 3.5mm sockets require TRRS plugs (not the standard TRS jacks that most microphones come with. TRS and TRRS plugs look very similar, so you need to find out which one your microphone has to know if you need an adaptor. All mobile devices have TRRS sockets. So you will may also need an adaptor like this:
For more detailed information on the difference between microphone plugs and sockets, watch this Youtube video.
There are other brands out there apart from Rode that do a good job, but I've found Rode to be the best, and they have a wide range of accessories, adaptors and cables to make most situations work.
Remember - try out the builtin microphone first to see if you can get the results you need, and then work up from there.