Use an Airtag/Apple Watch to lock an iPhone that's snatched in public?

I'd like to place an Airtag in my pocket (or just use my Apple Watch) and configure my iPhone to lock automatically when it moves out of range of the Airtag/Watch. This way, if someone snatches the unlocked phone out of my hands while I'm using it (e.g. sitting in a restaurant, on the street, etc.) then when they run way (with my phone!) and are far enough to break the connection with my AirTag/Watch, the phone will lock without warning.

Yes, I know I can force a lock using FindMy, but that assumes I'm carrying another iDevice or can quickly get to a computer to use iCloud. That's not easy while I'm out in public -- and a bad guy with my unlocked iPhone can cause a lot of damage before I can get to a computer to perform an iCloud login then lock the iPhone.

Is this something that I could do with Shortcuts?

Phone snatching is a thing -- there's got to be a better solution.

thanks.