If you really need a phone on you, get a burner phone with a prepaid card not linked to your person. But remember, MITM attacks are possible and the police can intercept your traffic and in some cases even compromise your E2EE services (if the key exchange takes place on a compromised spoofed network, see stingrays [1]).
If communication is necessary, get a meshtastic device. It's not the most reliable, and the channels can be jammed, but no one will bother with that. Because they work on usual IoT/smart home appliances frequencies, there is so much interference in cities that triangulating your position in a crowd of people isn't very realistic.
Clean install that bad boi (those 4a were done really well), update everything possible and then turn off as much settings/features as possible. It’s like reviving a 7 year old PC with Ubuntu 24.04.1(coming from an emotional standpoint than logical),the thing is badass again.
It’s a great offline device. Meshtastic, music player, eReader, remote, (use local non-two-way VPN) GPS, etc etc. to keep that device living longer for another 7-10 years, buy a replacement battery sooner than later.
Bringing extra meshtastic nodes to a protest could be really helpful. Extra nodes would allow information to more easily find a clear path out of a hot zone to routers in safer locations, and it’d do so without using any telecom infrastructure. The encryption’s pretty good too.