Considering how many data breaches have happened this year alone, I wouldn’t be very surprised if your phone number was leaked in one of them, along with your email address. Make sure you use unique passwords for all your online accounts (a password manager can help with this).
IIRC in recent years eBay made it so that if you are one of their “top rated” sellers, buyers can’t leave the neutral or negative feedback for a week. Which is nice and all for sellers that are trying to resolve any issues a buyer may have, but not nice for situations like this one.