Returning Values through HTTP Post within Infusionsoft Campaign API

Question

The specific objective here is as follows -

Using Infusionsoft API (iSDK), I need to create and host a file instructing infusionsoft to return the value of a 'Name / Value' pair from an HTTP Post to a contact specific Custom Field.

This is become increasing challenging as most of my experience revolves around HTML, CSS and basic Javascript and I am completely at a loss.

My HTTP Post url points to the following php file.

<?php require("isdk.php");
$app = new iSDK;
$connInfo = array(
"appname:appname:i:myapikey:appname.infusionsoft.com"
);

$returnFields = array('numberId');
$conDat = $app->loadCon('numberId', $returnFields);

$returnId = $conDat['numberId'];
$update = array('_customField' => 'numberId');
$conID = $app->updateCon($contactId, $update);





/*
And some additional code I don't know how to apply
$app->updateCustomField($, $numberId)
    {
        $carray = array(
            php_xmlrpc_encode((int)$fieldId),
            php_xmlrpc_encode($fieldValues));
        return $this->methodCaller("DataService.updateCustomField", $carray);
    }

*/