$biggest =100;
$all_numbers   = range(0,$biggest);
$threes 		= array_fill_keys(range(3, $biggest, 3), 'Fizz'); 
$fives 			= array_fill_keys(range(5, $biggest, 5), 'Buzz'); 
$fifteens 		= array_fill_keys(range(15, $biggest, 15), 'FizzBuzz'); 

$all_numbers 	= array_replace($all_numbers, $threes, $fives, $fifteens);

var_dump($all_numbers);