  Coherent time-delayed feedback allows the control of a quantum system and its
partial stabilization against noise and decoherence. The crucial and externally
accessible parameters in such control setups are the round-trip-induced delay
time $\tau$ and the frequencies $\omega$ of the involved optical transitions
which are typically controllable via global parameters like temperature, bias
or strain. They influence the dynamics via the amplitude and the phase $\phi =
\omega \tau$ of the feedback signal. These quantities are, however, not
independent. Here, we propose to control the feedback phase via a microwave
pump field. Using the example of a $\Lambda$-type three-level system, we show
that the Rabi frequency of the pump field induces phase shifts on demand and
therefore increases the applicability of coherent quantum feedback control
protocols.
