Anyone, YouTuber or otherwise, that says that the photographer must specialize in one specific niche is an idiot. I mean that’s like saying that in order to be a good mechanic you have to only work on one brand of car. I mean just like in that case, specializing in one narrow area might make you a little bit better at all of the subtle nuances involved in that area, but it’s not like having that knowledge mean that you can’t also have knowledge in other areas.
Personal feelings on the phone versus camera thing. Using a camera is what puts my brain into “photography mode” where I’m actually thinking about framing and composition and light whereas with my phone it’s more of a quick document the moment thing. Totally agree with the idea that the best one is whichever is available in any given moment though. While a thoughtfully composed image will be better than a quick grab,the quick grab is infinitely better than nothing at all.