Not all the time. Something you're entering, like name, address, phone number, or your ip address when you sign up is what's triggering the prompts to enter a phone number. Regardless of if the the prompt comes up though, to start selling you need a phone number. When those phone verification prompts come up even before you make the account, that's a red flag, something in their system already deem you as a risk and that's just a taste of the scrutiny that the account will face afterwards. If you don't mind the scrutiny, proceed with the account after the phone prompt comes up.
You'll also notice that something in their system considers something you entered a risk. Why would ebay ask ALL new members for a phone number JUST to sign up, regardless of what they're going to do with the account, whether it's buying or selling, that'd be inconvenient for customers.
| 
New eBay policy where you have to confirm your identity by phone just to make accnt? 
