For field service in dynamics 365, there is a mobile app that has been created using resco mobile framework. This helps a lot as the field engineers can do a lot of things from the fields using this app. Also the back office staff would get updates on how the job is coping up as well.
The mobile app has to be configured in Dynamics and it has to be carefully done.
Mitch has written a nice article on how this can be achieved. Please follow the link.