"Type In This Code To Prove You're Not A Robot"

Google and other websites had a great idea when they decided to make people type in a simple or hard code to prove that he or she is not a robot. The code would come up like you see in the picture i've provided and if said person fails to type it in correctly, said person will not be able to commence doing what he or she or it was about to do. This was a good idea to keep internet spamming robots out of sites like google, bing, etc. My idea is, if we could implement the same thing into our phones (make people type in a code in order to complete a call) this could stop the robo calls! Just like how a robot on the internet is incapable of typing in a code given by google or any other site. A robo caller will be incapable of typing in the code that's given to it. So I believe the solution to the robo caller problem is to take the route that google and many other sites have taken and make it so these robo callers have to type in a code to reach the person (which they will be unable to do). It does not have to be a long code like you see in my pictures, it could be a short code like "press 6 to prove you are human" The only time this wouldn't apply is when someone is calling 911. This will only apply to people calling other people. All they would have to do is press a certain number to prove they are human. Thank you so much for taking the time out to read my idea and I hope you all find it useful!