Add information to authorize.net transaction

<?php
// add additional information to authorize.net transaction
add_filter("gform_authorizenet_transaction_pre_authorize", "add_phone", 10, 4);
function add_phone($transaction, $form_data, $config, $validation_result){
    //get phone from post data, field id 8 for my field, change to your id
    $transaction->phone = rgpost("input_8");
    return $transaction;
}