Drag (air friction) is proportional to the square of velocity. If you know aerodynamic properties of iphone, you could find a value of velocity where drag is eq

Drag (air friction) is proportional to the square of velocity. If you know aerodynamic properties of iphone, you could find a value of velocity where drag is equal to gravitational force, at which point the speed doesn't change. You could use it as an approximation of the speed at which iphone hits the ground.