If you're a vlogger (or any kind of content creator), using your phone to film yourself is often the most logical solution. It's much more convenient and less conspicuous than lugging around a full-frame mirrorless setup, and you can enjoy a more natural FOV and better low-light performance than most action cameras, too.
The problem is, a phone's rear cameras are vastly superior to the selfie camera, so for the best image, you should be shooting with those. Unless you have a foldable phone, there's no way to properly frame your shot when filming yourself with the rear cameras. Sure, you could just guess, but I know from experience that this can result in some very awkward-looking shots.
