I use a flat piece of cardboard, folded with slots cut for the phone on top, and the monitor on bottom.

https://imgur.com/a/InImQFo

I just switched from an old apple cinema display to a modern monitor with small bezels, so I need to cut a new one to stop it from blocking the top of my screen.

These $10 selfie sticks with handles that open into a stand are actually great and much more compact and portable when closed than even a small tripod https://www.amazon.com/dp/B09B6QHZK5

I use this: https://www.monoprice.com/product?p_id=602507

Changed out the mount to work with my USB webcam and it works a treat. Obviously it won't work with a heavy mirrorless camera - but there are tons of mini tripods out there - the Joby Gorillapod's and their numerous clones are among my favorites due to their flexibility.

If you have one of the newer magsafe iPhones, you can attach one of these to the wall (front camera) or the back of your monitor (back cameras):

https://www.shopmoment.com/products/wall-mount-for-magsafe/s...

I've got a lego stand built from a few bricks holding an iPhone 7 in landscape above my screen. The lens is maybe 18mm above the top of the display pixels.