How to access phone contacts from PhoneGap in DrupalGap?
Here's the approach I would take:

1 - Build a custom DrupalGap module.

2 - Implement hook_install() in the module:

/**
 * Implements hook_install().
 */
function my_module_install() {
  sync_contacts_get_contacts();
}


3 - Create a Custom Service Resource Endpoint

4 - In your onSuccess function is where you would send the contacts JSON data up to your Drupal resource.

What (and how) you store the data in Drupal is up to you and your custom Drupal module(s).