array_multisort 关联（string）键名保持不变，但数字键名会被重新索引。

$array = [
    '2' => [
        'title' => 'Flower',
        'order' => 3
    ],
    '3' => [
        'title' => 'Rock',
        'order' => 1
    ],
    '4' => [
        'title' => 'Grass',
        'order' => 2
    ]
];

$keys = array_keys($array);
array_multisort(
    array_column($array, 'order'), SORT_DESC, SORT_NUMERIC, $array, $keys
);
$array = array_combine($keys, $array);

print_r($array);