How to make silicone iPhone cases? Where would you find the mold/outline of the iPhone?

How to make silicone iPhone cases? Where would you find the mold/outline of the iPhone? - 1

At a cell phone store

Measure the phone with a ruler. If your process of making a prototype is messy, you might carve a phone-shaped block to represent the phone. Other times you might incorporate your measurements into a 3-d model. Then once you have your prototype you can use that to make a mold in the shape of the silicone part.

You would need to have a solid block of metal
(aluminium or stainless steel, maybe; I'm not quite sure)
that was the exact size and shape of the phone.

How to get that is your problem to solve.

Then you would need silicone that can be molded
and some silicone-compatible mold release compound.

A bit of Google searching should get you well along your way.