True. If it were me who really cared about phoning home, I would buy a fresh iPhone, put it on its own WLAN from first boot, then record all packets from it for a month (plus some prodding of opening apps and changing settings). That should build a relatively comprehensive list of addresses to consider filtering.

Short of living in a shack in the woods, we will all have to trust someone at some point. I'm content to trust Apple to not lie on their documents, so the more important security and privacy checkboxes are ticked.