why is my new iphone asking me for six digit passcode?

That still doesn’t sound right. After Hello, it should go into a setup sequence, and one of the steps is to create a passcode. A new phone will not prompt you to create a passcode.

See this Apple support link→If you forgot the passcode on your iPhone, or your iPhone is disabled - Apple Support

Or watch this companion video ⬇️

This will put the phone back to its “new” state. Were you using Quick Start to transfer data from another device? If so it might have been asking for the passcode for that device.

The first time you turned the phone on did it display a screen that said “Hello”? If not, it was not a new phone. Return it.