Because of what a bid is.
When you bid, a seller stops. They hold the item up, the room competes, and at the end they put it aside for you and stop offering it to anybody else. That only works if a bid means something.
An account that cannot be traced to a person can bid freely and vanish freely. The cost lands on the seller, who lost the sale, and on the under-bidder, who wanted it.
What we do with it
Verify the account. Send you things you asked for — a win, a payment reminder, a delivery update.
What we do not do with it
Give it to sellers. Sell it. Send you marketing you did not ask for.
A seller sees your display name and, once you have paid, the delivery address they need to send the thing to. Not your number.
The verification itself
A six-digit code, valid ten minutes, five attempts. WhatsApp or SMS.
Questions people ask
Can I buy without giving a number?
You can watch without one. Bidding needs it.
Will I get marketing messages?
Not ones you did not ask for.
What if I change my number?
Tell us and we will move the account across. It is handled by a person on purpose, because an automatic transfer would be a way in for anyone holding your old handset. More on sign-in problems.
Who can see my number?
Us. Not sellers, not other buyers.
More: how to create an account, what Metzee does with your data.