RC, my doctor uses a switchboard however he gave a direct number extension for me to use as well as his home number.
My attorney gave me her private number, home number and her private cell number. So it depends on the doctor or lawyer.
I have noted on occasion calls from both offices change in the call number displayed. I normally just let unknown numbers go to voicemail and I return the call. Much easier.
I have noticed so called spammers use a rotation of numbers to try and get around a number block. The phone companies don't care because they make money from the scammers leasing the lines, and make money to have customers block them. It is a win win for the phone companies.