I read a paper on such a technique a while back. The CMOS sensors in smartphones are very sensitive to a certain band of infrared. I think it would be possible

I read a paper on such a technique a while back. The CMOS sensors in smartphones are very sensitive to a certain band of infrared. I think it would be possible to set up a system that automatically detects smartphone location and splashes its general area with infrared. With a good controller and motor setup, you could probably have a single jammer that can alternate between multiple phones.