Correct me if I'm wrong, but doesn't this interstellar swarm scheme require onboard clocks accurate to 1/frequency of the the light being used? Which is equivalent to the accurate measurement of phase.
They don't, see https://arxiv.org/abs/2309.07061 . The basic idea is to use "picosecond-level" synchronization to improve the signal-to-noise ratio. They mention that a truly phase-coherent swarm would perform much better but they consider that a longer term prospect (section 2.1.4).
