I really don't think you can avoid spam. At the end of the day, there are only so many phone numbers, and it's trivial to enumerate them to find those that are

I really don't think you can avoid spam. At the end of the day, there are only so many phone numbers, and it's trivial to enumerate them to find those that are live. Spammers can simply cycle through lists. Now if you're worried about more "targeted" spam, I would probably say do not pick the "business phone" option.