https://www.newsweek.com/us-russia-emergency-alert-drills-1831776
I think it's unlikely they're going to be broadcasting a 5G kill wave signal, or installing anything on your phone.
Announcing a declaration of full-scale war on the other hand? That actually seems more likely.
I saw someone here say for the entire day every electronic in the house would be in the microwave. If you are that worried leave it outside in a metal box or something. I'm turning everything off only if my grandchild is still asleep.