Hey Shredded, when I started out I was recording my audio separately via my phone.
I have a Samsung Galaxy S8+, I used the AKG headphoens that came with the phone, though I wanted it to be my dedicated mic so clipped off the earbuds so that it was a single wire running to my helmet.
Now whenever I record external audio I still use that same headphone mic but I record into an old iPod touch, there's a recording app that I found that allows you to adjust the gain and pitch so things like wind don't overload the audio file.
One thing I can tell you is make sure that you do a proper wrap on that external mic, use mic foam, then deadcat, and if you're like me add an extra layer to clean it all up, I used a bandana or microfiber cloth on mine.