The radiation exposure rate at the output phosphor will increase with:

The increase in radiation exposure rate at the output phosphor is directly related to the X-ray tube current. When the tube current is increased, more X-rays are produced, which means that a greater number of photons are generated and emitted from the X-ray tube. This increase in photon production culminates in a higher level of radiation reaching the output phosphor, leading to an increased exposure rate.

Essentially, the tube current controls the amount of radiation produced; therefore, a higher tube current results in a higher radiation output. This principle is integral to the functioning of fluoroscopic systems, allowing operators to adjust exposure levels as needed for patient imaging.

Options related to collimation, tube rotation, and filtration do not increase the radiation output in this way. Collimation focuses the beam but does not increase the dose, tube rotation is associated with imaging techniques rather than direct increases in exposure, and filtration reduces the number of low-energy photons that contribute to dose without increasing the overall exposure rate.