Which phase of flight requires the most active management of cabin pressure?

The phase of flight that requires the most active management of cabin pressure is during the climb. During this phase, the aircraft is rapidly ascending to its cruising altitude, and the pressure differential between the cabin and the outside atmosphere is constantly changing.

In the climb, it's crucial to ensure that the cabin pressure is maintained at a comfortable level for passengers and crew while also adhering to safety regulations. The cabin pressure must be gradually increased to match the decreasing atmospheric pressure outside as the aircraft ascends. This is achieved by the aircraft's pressurization system, which needs to adjust continuously and might require monitoring and intervention by the flight crew to manage the rate of climb and cabin pressure effectively.

Conversely, during takeoff, while the aircraft is beginning its ascent, cabin pressurization is already being initiated but does not require as fine-tuned management as in the climb. Descent involves managing pressure, but it's generally more straightforward as the cabin pressure is being released to equalize with the external pressure. Cruise involves maintaining a relatively stable cabin pressure, with less active management required compared to the climb phase.