Silicone mold for a telephone stand. The stand is 6 mm ( 1/4") thick and the space above the edge is 80 mm (3 3/5") wide and 130 mm (5 1/10") high.
The same mold is also available in a holographic version, see one of the pictures (for illustrative purposes, this item is only for the non-holographic mold).
There is also a mold available for an XL telephone stand, which is a good match for the larger (smart)phones. One of the pictures shows the size difference between the two stands.