Phone jamming technology is likely to be illegal, but you should check the laws for your local area. And you should obtain the advice of a local lawyer who is a

Phone jamming technology is likely to be illegal, but you should check the laws for your local area. And you should obtain the advice of a local lawyer who is approved to give local legal advice, etc.... I can’t do any of that for you. However, I can observe that there are passive means of blocking most radio signals (e.g., paint, wallpaper, aluminum foil, etc...), and those may not be illegal in your area. Again, you should consult your local lawyer.