The correct answer is: B. Decreases.
The phase response of a recorder noise level decreases with the bandwidth of a system. This is because the phase response is a measure of how much the phase of a signal is delayed as it passes through a system. The wider the bandwidth of a system, the less time it takes for a signal to pass through the system, and the less the phase of the signal will be delayed.
Option A is incorrect because the phase response of a recorder noise level does not increase with the bandwidth of a system. Option C is incorrect because the phase response of a recorder noise level does not reach unity with the bandwidth of a system. Option D is incorrect because the phase response of a recorder noise level does not reach infinity with the bandwidth of a system.