I found a fix. Apple apparently added a feature called "Center Stage." You seem to need that to get back to using the main rear camera...
After you select and start your iPhone's camera via FaceTime, Zoom or other VC apps, there's a green camera indicator on the menu bar, just like the mic recording indicator but for video. Click that, then the "expand down" arrow next to the camera name. Then enable "Center Stage" from the four or so options.
That zooms you back in, dynamically, using the wide-angle camera by default. So it's probably going to be lower res than before. To fix that, click the "expand right" arrow and pick "Main" to get back to using the main camera vs. the wide-angle one. It still pans and zooms automatically, but video quality is close to before, closer to DSLR, IMO, but autofocus is not always right.
There are some other options like "Studio Light" and automatic background blurring "Portrait" mode you can try. "Reactions" is kind of wild, but hard to use when it's this far down.
I can understand why they added this mode, since Continuity Camera now supports Apple TVs. So you need to potentially get the whole living room in view for FaceTime with Grandma.
Still, I'd prefer if "Main" was selectable without Center Stage. I can center myself manually on a VC call. Maybe they could add a manual zoom and focus slider here too to make it truly DLSR competitive?