This is an Ikea Skadis T-Clip compatible Livboj cradle. It fits the Livboj and an iPhone. Most likely other devices as well, but I didn't test.
It's sturdy enough (even on the draft quick print with untuned filament on the photo).
Leaves enough space for the iPhone to make it comfortable to put in and take out. The Ikea USB-C wire also fits nicely in there.
The author marked this model as their own original creation.