Add phone and custom fields to custom ticket form with the Ticketing API

Hi Zendesk's community,

When following this guide: https://developer.zendesk.com/documentation/ticketing/managing-tickets/building-a-custom-ticket-form-with-the-zendesk-api/

Is it possible to add a phone number to the requester's object and access the user fields (*.zendesk.com/admin/people/configuration/user_fields).

Thank you!