For maximum strength and minimum chance of breakage, print at .1 layer height, 1 shell, and 100% full honeycomb infill. And, even though it's sturdy, treat it with a bit of care! You don't want the post to break off inside your headphone jack!!
It prints all as once piece and moves straight off the print bed. Push it gently into the headphone jack as far as it needs to go to spin freely - without touching your case.
This was designed from the idea of an Oregon State University student who "always fiddles with her phone case while studying" :-)
BE SURE TO PRINT IT AT .1 LAYER HEIGHT, 1 SHELL/PERIMETER, AND 100% FULL HONEYCOMB INFILL, and though you don't have to creep along, don't have it go super fast, ok? It doesn't take long to print, even with these settings. This might possibly be the World's Smallest Fidget Spinner!