I had a similar concern where my number might be known to an adversary but the site I was using had to use SMS validation. So, I tried rolling a solution for this problem with Twilio but the range the number was assigned from was blocked because I guess others have had the same idea and used it to abuse the service.
I guess I'd propose that a company phone is allocated and kept in an office somewhere, not ideal though as it's a single point of failure.
Twitter however is reasonably rare in that you can't create subaccounts for individuals, most B2B products will let you do that.
An industry has sprung up around this however and there are Twitter management services however that will hold the credentials for you and allow you to accounts for named users etc.