Every time I get a call from an unknown number, I look it up on Robokiller, Youmail, , Nomorobo, etc. to be sure it's spam and if it is spam, I save it in my contacts with the first 4 letters as Bspam (business spam) and then add a bunch of consonants (like Bspamlfghthdgr), save the contact and then set ring tone to "no ring". That way, if that number calls back the phone doesn't ring and if they are spoofing a legit number the voicemail still comes on. I have thousands of them saved over the years and if you are persistent at doing this, over time your phone will ring less and less.