With this function your phone will automatically raise the ring volume if it detects that the same person is trying to call you and you have not answered the call.
The ringer volume of your phone will be set to maximum if the same telephone number repeats the call in an interval of less than 3 minutes. After answering the call, your phone's volume will revert to the previously preset volume.
You can enable or disable it via "Settings> Smart Help> Smart ringer.