Regarding how to point the phone: if it's an iPhone, voiceover should tell you when it sees faces. Even better would be to use Seeing AI, for more detail. You wouldn't do this while recording, of course, but use it to learn how it works. Then maybe try taking pictures and get Seeing AI to identify them, and the closer to what you intended, the better. Once you're good enough at that, you should be able to do it without spoken feedback.
It sounds like the phone is stationary, so it seems likely that there was some testing to determine the best position, then it's just a matter of reconstructing the setup (big, unmoving furniture is great for this).
If you're using a webcam, laptop built-in camera, an Android, or iOS11, you could use the vOICe. Yeah, it takes a ton of practice to use it for detailed information, but you don't need that; you just need a general idea. Keeping the camera stationary, then moving around and listening for changes, is enough to figure out some basics about where you are on the screen, etc. It's far from fool-proof; I tried this with an elaborate setup involving a Ninja Turtle and construction paper, (and it was Michael Angelo, which matters because orange), and while I got a picture of said Ninja Turtle, close to center, not much of his legs were in frame, which I only found out when I put the photo on Facebook to ask if my predictions (I was testing other things, too) were correct. (They weren't, because I couldn't distinguish the orange in Mikey's bands from the yellow-orange of his chest/abdomin with Iodimony.)
Ultimately, easiest will be to get sighted help, but if you can't / won't go that route, something in the above should help. Maybe. Hopefully.

This is my same setup for making videos too glad to see someone else use the same methods.  I use sighted help for lining up the video though, I'd be interested to hear in more detail how this AI thing works for positioning - is there anything to download onto your PC to do this with?  I use a webcam when I record video, but I do visualization videos for my videos that I'm just doing oo and aaaah sounds with on my video game covers.  Kind of fell off the wagon with recording myself on cam though, need to get back into it lol.  Hope we can all share good tips in this thread and see what we all use!

Also yeah I line up the two audio sources and make sure they are in sinc, and that's how I make sure my videos look ok because I always record video after audio.  Pretty easy to do in Reaper

The visualization method is great for when you just don't  have a reason to do a full fledged video lol.  That and using stock footage are my two go tos when I just want to put something quick together in movie maker, but I do want to try using OBS to record a Reaper project.  Do you just use window capture?