I mean, I can just video things with my phone or course, but was hoping to get good audio quality at the same time. I have the gear to do that with. It shouldn't be difficult to get both into one format, and sync'd, given the technology available. It shouldn't require lots of other gear and software.
Multiple apps aren't necessary. It doesn't require lots of other gear and software at all. It does require a DAW that works with picture, and plenty of them do.
It is simple, if you use Logic (and other DAWs will do this, too, but I'm most familiar with Logic, though my partner uses Cubase and Nuendo to do the same things); ProTools will also do this, as will DP.
As you know, scoring to picture is what I do, and I work to picture. I also send my work to clients with picture - that's what I have to do for approvals on tracks or audio post mixes. Clients send me picture and revisions from video post facilities every single day, sometimes multiple times a day. I don't have time to screw around with two apps.
So:
Let's assume for the moment you know how to email or using bluetooth or your wifi send a video file from your phone (or export it from your phone into a file sharing platform). Import it into your computer. Should take a few seconds at most.
If you're working in Logic, there's a menu item to open a movie. You can also click the dialog box to import any audio already recorded onto the video in one single step. Logic will automatically create a new track with the movie audio, that you can use, or not, depending on your needs. The movie opens in a window in your DAW.
You can set the tempo, record new audio, move the audio, do whatever you want easily, without messing up the sync with picture. No slates needed.
When you've got the audio to your liking in Logic, simply choose "Export Audio To Movie."
Boom. Done. You now have your movie striped with whatever you've done in your DAW. If your DAW doesn't have the ability to work with video, there are many others that do. Get one of them.
If your phone's mic sucks, Shure and others make inexpensive mics for them that clip right to the phone. I had my daughter get one to record my granddaughter's audition videos for pro theater stuff. There are also audio interfaces that work with phones if you want even better sound, but I'm pretty impressed by the little Shure mic.
Point is, it is ridiculously simple to do what you want to do.