Maintaining phase continuity of LO when switching from Tx to Rx mode
This is readily achieved, by either

a) using a design which utilizes the same oscillator and oscillator frequency for upconverting signals as it uses for downconverting, such the that the local oscillator does not need to change frequency when switching modes.  This will work best with an IQ design where the target frequency falls at 0 Hz on the baseband side, or at least would +/- any error.

b) using entirely distinct transmit and receive paths, such that the transmit LO never changes frequency, and perhaps that the receive LO is phase locked to the same source and you are able to receive some siphoned off transmit energy to perform a reference phase comparison.

However, your question is a bit incomplete on the surrounding details likely necessary to obtain the actual benefit of such steps.