This is a case for the Satechi Bluetooth media remote that simply adds a clip on the back.
The Satechi remote adds wireless media controls to your mobile phone; I personally find it very useful to use with my Apple AirPods, since they don't have a media clicker like Apple's wired earbuds do. This 3D-printed clip-on holder lets you clip the remote onto your shirt/bag/etc, making it easy to access media controls wherever you are.
The raw model / CAD file is available on OnShape
The design is simple enough that infill/resolution settings shouldn't really matter.
Supports aren't needed, and (at least on my cheap printer) were a pain to remove.
Immediately after printing, you may need to manually clean up the whitespace between the triangle clip and the main base.
To use, just pop the clicker in. Make sure you pair it first, as you won't be able to access the pairing button when it's inside (and the current design makes it very difficult to remove).