Its a pretty straight forward technique, the display is at the bottom and in the glass cube there is a mirror at 45 degree angle facing you (you can see the mirrors edge on the side wall) which reflects the image from the display at the bottom making it look like a hologram

You can create the same effect on a smart phone screen with a video like this: https://m.youtube.com/watch?v=CIszi2Kv_lk and a some clear plastic sheet put together like this: https://www.twowaymirrors.com/wp-content/uploads/2019/11/pep...

OP: beautiful work with your surf projector!