There's no way it's 20-40 mph. They're dense enough for much higher velocities.
Of course that assumes it’s falling facing its largest surface, and not tumbling or a falling edge first. Obviously that is trickier to calculate, but 20-40mph doesn’t seem that unreasonable.
Edit: it takes ~3 seconds to reach 99% terminal velocity.
That was what I was thinking: surely it wouldn't be stable falling face-first? Wouldn't it be more likely to either tumble or settle on an edge?
There's also the possibility that it behaves more like an airfoil, and starts generating lift once it's going fast enough.
https://www.wolframalpha.com/input?i=terminal+velocity+of+an...
putting mildly, still it's lovely to see the mix the input of imperial and metric units.
the 'fluid' density is quite wrong as well. 1.29 kg/m^3 -> almost 777 times lighter than water, it's similar to air. By its dimension iphone 15 should be around twice heavier than water.