Accessing/storing values from JSON serializeArray() in PHP

Question

I give up. I'm sending form data to PHP via ajax using json.serializeArray().

In it's raw form it arrives like this:

["0":{
    "name": "first_name",
    "value": "BILLY"
    }, 
"1":{
    "name": "phone",
    "value": "04532423"
    }
]

In PHP, I'm trying to store/access the values. So I loop through using something like:

$new_data = array();
for($i = 0; $i < count($data); $i++) {
  $obj = new stdClass();
  $key = $data[$i]['name'];
  $val = $data[$i]['value'];
  $obj->$key = $val;
  array_push($new_data, $obj);
}

Which results in:

[
    {
        "first_name": "test"
    },
    {
        "phone": "0422335656"
    }
]

I then try to simplify the array further using a function:

$form_data = $_POST['order_details'];
function simple_merge($data) {
    $new_data = array();
    $new_obj = new stdClass();
    for ($i = 0; $i < count($data); $i++) {
        $obj = new stdClass();
        $key = $data[$i]['name'];
        $val = $data[$i]['value'];
        $obj - > $key = $val;
        array_push($new_data, $obj);
    };
    foreach($new_data as $key => $value) {
        $new_obj - > $key = $value;
    }
    return $new_obj;
}

$response = simple_merge($form_data);

echo json_encode($response);

Which should result in a single object I can access using something like $data->[$key] but the results are returning as null.

I've tried simplifying the form data to JSON before sending it, but am having similar results.

For more context, I'm trying to create a new order in WooCommerce, and to debug I'm storing the results in an object and then returning them using echo json_decode($response)

I have a feeling that this is one of those problems where the solution is going to have me facepalming.