This is a mounting bracket for the RAM-B-102-UN10U found here: https://amzn.to/4aFCtgC (you supply the RAM mount).
It is laser cut 10ga polished stainless steel. This bolts in-between the grab handle and door frame. Factory hardware can be re-used, but the first 4 orders of this new product will receive complimentary new silver zinc hardware.
 
This was designed for a 2013 CAT 312E excavator, HOWEVER, the 312-320 should all share the same cab. It may also fit newer models such as the "F" and "Next Gen". It may also fit older models. Please contact me if you'd like to verify fitment before ordering.
 
This positions your phone conveniently to your left side without restricting access to your door handle. You can comfortably turn your head to the left, view your phone, and use your phone with your right hand.