Hey, not to discourage you at all, but from what I can tell most viewers are a bit bored by watching episodic Factorio videos. I would recommend creating longer-form videos that encompass your entire challenge rather than an entire series of it. It's a lot less video output for the effort you put in, but you have the advantage of being able to narrate the entire challenge as a story. If you want some good examples of this, check out Dosh Doshington's content. He doesn't post too often, but when he does it always does well.
If it's available for you you could always stream instead. A lot of people will stream Factorio live, then assemble a narrated video for YouTube from the VODs.
Doing a quick skim on my phone, your microphone quality is fine. I would probably lower the game audio in post a bit to make the sound more distinct, but it's only noticeable when the game does loud stuff.
I watched it on my phone in 1080p60 and the scale didn't bother me. It's not like I have to read a lot of text and the precise position of the player character is mostly irrelevant, too. Like, if you get hit by a train or something, the screen will flash red and you'll react to it, too, so I'll know what's going on.
Well, and I don't look at the screen at all times anyways. 🙃