Maybe this helps wrapping your had around the start-suspend-resume-return circle:

$fiber = new Fiber(
    function($one) {
        $two = Fiber::suspend($one);
        $three = Fiber::suspend($two);
        $four = Fiber::suspend($three);
        $five = Fiber::suspend($four);
        $six = Fiber::suspend($five);
        return $six;
    }
);

print $fiber->start(1);
print $fiber->resume(2);
print $fiber->resume(3);
print $fiber->resume(4);
print $fiber->resume(5);
print $fiber->resume(6);
print $fiber->getReturn();

//prints 123456