Under what condition should a boat operator avoid using a mobile phone?

The correct choice highlights the critical importance of maintaining full attention on navigating or operating the vessel. When a boat operator is using a mobile phone, their focus is divided, which can lead to dangerous situations on the water. Navigating requires constant awareness of the surroundings, such as other vessels, navigational markers, and potential hazards. Distractions from a mobile phone can significantly impair an operator's ability to react quickly to these factors, potentially resulting in accidents.

In contrast, managing onboard passengers, maintaining equipment, or mapping out a route may involve moments where the operator could safely delegate attention or perform other tasks without compromising the immediate safety and control of the vessel. However, while all these activities are important, none should take precedence over safe navigation practices. Therefore, refraining from using a mobile phone while operating the vessel is crucial for ensuring the safety of everyone on board and nearby.