Haha yes James/Dave. I’m very lo-tech with recording. I admire and respect all the others with their DAWs and multitracking of course but other than posting here for a bit of feedback, my recordings aren’t going anywhere, so a phone is good enough. It’s beyond me why others have more as this is essentially a beginners website/forum. I’m now ducking my head to avoid the inevitable onslaught of replies 
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The first thing is to get the video framed the way you want it. For constructive feedback you need to show your fretting hand and strumming hand in the frame. Including your head is optional! 
I’ve found that strumming and singing in a ‘normal’ way works pretty well after that.
The exception to this is if you use a backing track or a loop or whatever through an amp because the built in phone mics are designed to pick up the closest sounds.
I have a Trio+ looper/backing band creator. If I use that through my amp I need the amp volume pretty high so the phone can pick it up. It’s then a case of experimenting with your vocal and guitar volume to get the balance right.
Now, if I only knew how to work a DAW.
Edit : Have a look here. Home Recording
If you’re short of a rabbit hole to go down then here’s one!