This is already mostly done.

Participate in the development of Reticulum. Install the app Sideband on your Smartphone or other device.

Sideband is a chat app that uses LXMF. LXMF is a messaging protocol based on Reticulum. Reticulum is a full network stack that is decentralized and transport layer agnostic.

What we need for your vision is LoRa modems integrated in our phones.

Or just a bluetooth mesh interface for Reticulum. That is a great idea. Develop that, and you have exactly what you described.

To be more specific: Reticulum's main program is the daemon rnsd. It uses so called interfaces and can route between them (WiFi, LoRa, other radio services...). Implement a new interface type that uses the technology called 'bluetooth mesh' and your vision is done.