$array = array_fill(0, 2, array_merge(
   ['hello'],
   ['by']
));

var_dump($array);

array(2) {
  [0]=>
  array(2) {
    [0]=>
    string(5) "hello"
    [1]=>
    string(2) "by"
  }
  [1]=>
  array(2) {
    [0]=>
    string(5) "hello"
    [1]=>
    string(2) "by"
  }
}

array(4) {
    [0]=>
    string(5) "hello"
    [1]=>
    string(2) "by"
    [2]=>
    string(5) "hello"
    [3]=>
    string(2) "by"
}

$values = new ArrayIterator(['hello', 'by']);
$cycle  = new InfiniteIterator($values);
$limit  = new LimitIterator($cycle,0, 4);

$array = [];

foreach ($limit as $value) {
  $array[] = $value;
}

var_dump($array);

array(4) {
  [0]=>
  string(5) "hello"
  [1]=>
  string(2) "by"
  [2]=>
  string(5) "hello"
  [3]=>
  string(2) "by"
}

$array = array_merge(...array_fill(0, 2, array_merge(
   ['hello'],
   ['by']
)));