I think Google offers free phone numbers through Google Voice. As far as I know, you can port in numbers too, so if you really wanted, you could get an inexpensive prepaid plan then transfer it to Google. (but I doubt there will be a problem using the Google Voice number that is assigned for free)
I think all 3 are likely detectable.
AdNauseam is my favorite though, and probably currently the least detectable. It purposefully costs advertisers the money they bid against each other for clicks. Though, if abuse of it becomes too high, I think Google would very likely separate out users they have detected as likely bots. Though, for people who do not browse the internet very often, there might not be very much data to be confident they’re a bot.
I really don’t like that modern advertising is based on highly invasive spying. A billboard is a nuisance, but someone watching everything I do online is a stalker.
edit: It’s about making predictions about behavior worse. An issue is that advertising has conversions or sales, which most fake clicks will not become conversions… but part of it is just creating data that might cause predictions against other people for content they don’t desire. (resulting in less impactful advertising)