Which phase represents the time when field units are responding to an incident?

The correct choice is the response phase, as this term specifically refers to the period when field units are actively engaging with a situation. During this phase, emergency personnel such as police, fire, or medical teams are dispatched and en route to the incident location. This is a critical time when various factors, including resource allocation and situational assessment, come into play.

The call receiving phase focuses on the initial communication where the emergency situation is reported and assessed, but it does not involve any action taken by field units. The post-response phase occurs after the incident is managed, involving activities such as documentation and follow-up, while the emergency response mode is a broader term that may encompass various operational protocols but is not specific to the moment when responders are en route to an incident.