How to disable SMS for two factor authentication?
Unfortunately you cannot disable the feature.
Your best bet is keeping the number used completely private. I.e. do not use your main phone number for this - use a number specifically reserved for 2FA codes so that this phone number is not shared with others.
Also I would like to point out that the loophole described in the link you have included has actually been closed shortly after that article was written through a collaboration between T-Mobile, Verizon and AT&amp;T.
However it is still true that if you have some other means of providing a second factor than SMS, then you should definitely go for that instead. SMS is the least desirable of all options.