Retrieving shipping phone number at checkout

[KvnSpy]

Hello,

I'm developing a PHP payment app, redirecting to a third party payment provider.

But during  the payment process, after the checkout page, it seems the shipping phone number is not passed into the request. Here is the request object I get :

array (
'id' => 'rFLtDq0ak31PF0dh4t3vZUz4p',
'gid' => 'gid://shopify/PaymentSession/rFLtDq0ak31PF0dh4t3vZUz4p',
'group' => 'D2R56Gdzq8MZeFgI6nuNRmWCkB/pS5X16+jsLI6+0wI=',
'amount' => '20.8',
'currency' => 'EUR',
'test' => true,
'proposed_at' => '2023-04-18T08:40:31Z',
'kind' => 'sale',
'payment_method' =>
  array (
    'type' => 'offsite',
    'data' =>
  array (
    'cancel_url' => 'https://my-test-store.myshopify.com/checkouts/c/0c43c0c1946b46bf2099e728fb25fa8e/processing',
  ),
),
'customer' =>
  array (
    'billing_address' =>
      array (
        'given_name' => 'John',
        'family_name' => 'Do',
        'line1' => '40 rue de Moscou',
        'line2' => '4b',
        'city' => 'Paris',
        'postal_code' => '75008',
        'country_code' => 'FR',
      ),
    'shipping_address' =>
      array (
        'given_name' => 'John',
        'family_name' => 'Do',
        'line1' => '40 rue de Moscou',
        'line2' => '4b',
        'city' => 'Paris',
        'postal_code' => '75008',
        'country_code' => 'FR',
      ),
    'email' => 'j.do@gmail.com',
    'locale' => 'en-FR',
  ),
'cancel_url' => 'https://my-test-store.myshopify.com/checkouts/c/0c43c0c1946b46bf2099e728fb25fa8e/processing',
'merchant_locale' => 'en-FR',
)

 when fullfilling the checkout form as this : 

Note that I correctly get the contact information (should it be email or phone number), but not the shipping one.

Any ideas on how to retrieve it ?