Did you read the article? The victim who've had their phone number stolen weren't the ones that fell prey to social engineering - it's the customer service people at the phone provider who are persuaded to do a port of the phone number.
Unless you operate your own phone carrier, it would be hard to avoid this attack.
How, exactly, would you prevent someone in a call center on the other side of the world from being convinced to port your number away?
Outgoing port "blocks" are nothing more than a note in your file - what's to say that the attacker couldn't just make up a story? "I know I called a while back and asked you to prevent porting, but I really want to switch to X carrier to get their exclusive new handset. Can you remove the block request, my mothers maiden name is..."
Pretending like you could prevent this sort of attack is laughable, which is why it's so dangerous.
As I said, like the DNS system : you lock the number, only allowing porting upon presentation of a secret that only you know. Default state is : locked.
Unless you operate your own phone carrier, it would be hard to avoid this attack.