step() feels very inelegant

fizzBuzzGen.php

<?php

$fizz = function() {
    while(true) {
        yield '';
        yield '';
        yield 'Fizz';
    }
};

$buzz = function() {
    while(true) {
        yield '';
        yield '';
        yield '';
        yield '';
        yield 'Buzz';
    }
};

function step(\Generator $gen) {
    $value = $gen->current();
    $gen->next();
    return $value;
}

$fizzGen = $fizz();
$buzzGen = $buzz();

foreach(range(1,100) as $i) {
    echo step($fizzGen) . step($buzzGen) ?: $i, PHP_EOL;
}