  The delay of photodetectors can be affected by intensity, reverse bias, and
temperature through different effects. An optical pilot tone superimposed on
the detectors allows the independent measurement of such phase errors in the
complete photodetection chain and provides an opportunity to correct them. This
allows further separate readout noise from the measurement, providing a more
performant and intensity-invariant phase readout. We test the functional
principle on a setup demonstrating an improved phase noise performance and a
reduced phase walk below 10~mHz in particular. This benefits applications which
require accurate timing or signal phase determination with photodiodes.
