$form_params = array(
    'id' => 1,
    'ids' => [1,2,3],
);
$form_params = http_build_query($form_params);
$form_params = preg_replace('/%5B[0-9]+%5D/simU', '%5B%5D', $form_params);

参考

• http_build_query — 生成 URL-encode 之后的请求字符串