This option needs to be a lot more widely adopted.
Discussion
The correct answer was "I don’t need to give you a reason why"
GFY would have been better
Whenever I've needed to answer that on the gov website I've just said "I won't pick up" 😂
Demanding phone numbers is usually an act of evil, sometimes of ignorance. If they refuse your VOIP number, then it's definitely evil. Email should be enough. It's trivial to have a truly private email address.