Steve, I posted the following on YouTube regarding your video "Using portrait 9:16 phone video in a landscape 16:9 Premiere Elements project". But, decided to post it here too.
I'm working with a portrait video taken with a phone. I thought I followed every step you showed in your video, but the black border is still there. I've confirmed that the bottom video is scaled to 320 by blocking the top video from showing. Since I first tried using that technique in a project that I had already started, I thought maybe I'd done something to prevent this technique from working. So, I started a new project involving just the video.
I'm working with PRE 2020 and have your "The Muvipix.com Guide to Adobe Premiere Elements 2020", but didn't find a reference to this procedure in there. Thanks for your great help!!!