I was under the impression that the iPhone needs to be very precisely pointed at a satellite for this to work. I doubt it can be done passively when the phone is in your pocket.
You can't even realistically point the InReach Mini at a satellite because it doesn't tell you where they are. At any time there's only a couple of iridium sats in view and they move quite fast across the sky.
But the device has an antenna with the right amount of upwards gain and the right polarisation to deal with that. For an iphone it's a lot harder to incorporate that.