Just to have this here in the support part, where more people can see it:
Jetpack crashes iOS Safari on iPhones (tested on different iPhone models). It only happens nearly every time, so it may be a bit difficult to notice.
Not nice, but the buggy part of Jetpack is the comment feature. You can deactivate the Jetpack comments and the problem is solved.
(I hadn't realized it is possible to deactivate just the comment part)