There's so many great versions of this contraption, but this is my favourite one, as it's both simple and stable.
Step 1: Materials
You will need:
Two extra large binder clips (1" or larger)
One slightly smaller binder clip
Step 2: Form the base
Start with your two large clips. With "mouths" facing, slide one arm of a clip over the other. This is the main body of the stand. Your phone will rest on the arm that's sticking up.
Step 3: Add the headrest
With your smaller binder clip, slide one arm into the prone arm of the larger clip (i.e. the one that's not sticking up). Now, clip it to the top of the arm that's sticking up. This is your phone's headrest.
Step 4: Finished!
Enjoy your new smartphone stand! Just don't display it too prominently at your desk. It invites speculation that you do not have enough to do.