In the Data 360 Trailhead project, Contact_Home has no “Phone” field. It only has Asst. Phone, Business Phone, Home Phone, Mobile Phone, and Other Phone. Which field should I map to Formatted E164 Phone Number?

@VADAGLE SUNNY PAUL - Formatted E164 Phone Number  is a field in Contact Point Phone data model object. You should add this object on the mapping screen by clicking the pencil icon that says Update target entities on the top right hand corner of your list of data model entities and complete the mapping from the DLO to the DMO. As @Keiji Otsubo mentioned, you did not specify the trail/module you are working on so it is hard to say which field should be mapped but if I recall correctly, it is the Business Phone field in Contact_Home that is mapped to  Formatted E164 Phone Number in Contact Point Phone.