Not every call we get is spam. So make sure you use this with care, otherwise you could end up silencing important phone calls. This feature does not block people from calling you, but it stops your phone from ringing and sends everyone who is not a contact in your phone book to voicemail. This can be a great tool if your phone number is inundated with robocalls and spam.
To enable this new feature, make sure you have iOS 13.0 or newer installed and follow the path below.
Settings --> Phone --> Silence Unknown Callers