how conventional a phone is this intended to be and what does the target market expect?
how much can you stuff inside the device, taking into account physical space, heat dissipation and power consumption?
You will note that the first link above implicitly talks about taking out the cellular modem and replacing it with a LoRa card. That’s a good feature of a modular design. You are free to do that.
Would it work? Who can say but I would kind of like something that just makes conventional phone calls before exploring the full potential.