If you run a bit into the edge of a counter top, with 70 lbs of force, I feel, your phone would not be your top concern. Plus I think, people are mostly worried about the phone deforming in your back pocket if you sit down on it. I am not a physics student, but even if you sit down on, say concrete, I think, your ass needs to have some serious muscle tone, such that a metallic object can get deformed without causing you discomfort.