You can't do that I am afraid.
As you say, Ebay do ask for your mobile number and then, every time you buy an item, they pass your number on to the seller you have bought from.
Has it been an issue?
Personally, in 20 years, I have never phoned a buyer or had a phone call from a seller I have been in a transaction with.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)
