An app called "Nomorobo" grew out of one such contest. The company's website says the app works by scanning all incoming calls against a list of known problem numbers to catch robocalls at a cost of $1.99 per month. The FTC says there are many other apps available. 5. You can put your phone on "do not disturb" mode This move will block all but your known and trusted numbers. But if none of that works – then it might be time to change how you use your phone. "It's tough,” Michael Self, a former robocaller, said. “They're gonna get through." The best thing you can do, he says, is to "be aware, and be skeptical."