curl https://api2.ecomailapp.cz/lists/789/subscriber-by-phone/+420777888999 \
  -H "key: YOUR_API_KEY" \
  -H "Content-Type: application/json"

$listId = 789;
$phone = urlencode('+420777888999');
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "https://api2.ecomailapp.cz/lists/{$listId}/subscriber-by-phone/{$phone}");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, [
    'key: YOUR_API_KEY',
    'Content-Type: application/json',
]);
$response = curl_exec($ch);
curl_close($ch);

{
  "subscriber": {
    "id": 123456,
    "list_id": 789,
    "email": "foo@bar.cz",
    "status": 1,
    "subscribed_at": "2023-01-01T00:00:00.000000Z",
    "custom_fields": { "id": "123" },
    "source": "API"
  }
}

{
  "errors": { "phone": ["Invalid phone number"] }
}