The contact details that you have loaded in your Account setup can be used in the Route Builder, Planner and Review steps of the Itinerary Builder wherever you see the 'Load Contacts' button appear.
**In the Route Builder Step**
The option will be available on the majority of the Mode of Transport with the exception of Self-Drive, Scheduled Flights and Hike.
To add your loaded contact to your selected 'Mode' of Transport, select the icon next to your transport type and click on the 'Load Contacts' button.