HP OOP builder pattern use

I'm confused about using PHP Builder pattern in practise. In many documentation they propose using the Builder like this.

require 'Pizza.php';
require 'PizzaBuiler.php';

$piza_builder=(new PizzaBuilder('medium'))
        ->cheeze(true)
        ->bacon(true)
        ->build();

$pizza=new Pizza($piza_builder);

Pizza class use PizzaBuilder as constructor parameter and init class properties from it.

Why not instantiate object directly from Builder ??? is this bad (Anti-Pattern).

require 'Pizza.php';
require 'PizzaBuiler.php';

$piza= Pizza::getBuilder("medium")
        ->cheeze(true)
        ->bacon(true)
        ->build();

The only difference between two implemnettations is to modify build() function in Builder class to return new Pizza Object instead of of returning Builder instance.

can you advice me what clean builder to use ???