I carry an InReach mini in my airplane when flying over wilderness areas. Unfortunately I don’t think I could trust the iPhone. With the Garmin you can press one button and it’ll send out an emergency beacon without having to aim it.
There are lots of great places to land, but being stuck in the desert without any way to communicate is a very real possibility (Ironically, even at many small town airports I’ve landed at).
That said, aircraft have ELTs which are supposed to trigger on impact and can be manually activated as well, so an InReach probably wouldn't make a life-or-death difference very often.
And for a dedicated device, the tracking feature is laughably bad with worse accuracy than my friend's watch.
Better than nothing in case of emergency but the reliability leaves a lot to be desired.