What phrase indicates that flight attendants must immediately take their seats during turbulence?

The phrase "Flight attendants, be seated immediately" serves as a direct instruction to flight attendants, indicating that they must take their seats without delay during turbulence. This specific instruction emphasizes the urgency of the situation, ensuring the safety of both the crew and passengers.

When turbulence occurs, it is essential for the flight attendants to be seated securely to prevent any risk of injury, as during such events they could be thrown about the cabin if they remain standing. This phrase provides clear, unambiguous guidance to crew members in a way that highlights the immediate need for safety measures.

Other phrases might signal preparation for various scenarios, but they do not convey the same immediate action focused on the safety of the cabin crew during turbulence as clearly as this specific instruction does.