To activate Smart Blocking on an iPhone:
1. Open up your YouMail app
2.Make sure you are in your History tab 
3.Tap the caller you wish to block
4. Tap on the 
icon underneath the phone number
5. Tap Report Spam
You have successfully blocked a caller with YouMail’s enhanced Smart Blocking! YouMail greets blocked callers with a message of your choice, such as a "This number has been disconnected."
Learn how to enable iPhone's built-in call blocking software.