Any way to enforce it ?
Probably not. Some of it will probably involve the Rov hounding repeat offenders.
Just want to point out that blocking signals doesn't mean they won't be able to use their phones at all. It'll eliminate the noise perhaps, and some people don't do much on their phones that doesn't involve internet connectivity - but it's not a full solution. The only full solution is not to have it in shul at all.
There's a guy I see in shul every so often that davens shmona esrai in a minute or two, and then sits down and plays some sort of candy crush type of game. And this wasn't a one time occurrence.