Here's a deeper dive on that question:

https://naehrdine.blogspot.com/2024/11/reverse-engineering-i...

Tl,dr: it's likely baked into the sep, no ntp

I'm wondering if you put the phone into a mode where it thinks it's dialing emergency services or contacting them via crash detection etc that it won't reboot. I could picture a scenario where the code is written to never disrupt an emergency services call.

Full disclosure I don't own an iPhone so this may not even be a thing. Just guessing based on liability risk from Apple of "what's more important than protecting the phone"