Looking for this stl design for a cellphone clamp
This file simply is not on Thingiverse. Not all files are on Thingiverse.
A Google reverse-image-search for that picture in all size told me that the image stems from an all3dp article, and they have a reference link to Pinshape as it is presented here:

The file name of the linked picture is universal-phone-tripod-mount-3d-printing-155113.jpg
Taking that as a search term lead me to pinshape model 37196: 3d printed universal phone-tripod mount by jakejake