Liquid nanocrystal microlasers are promising miniaturized coherent light sources, yet their development remains constrained by the difficulty of simultaneously preserving colloidal gain media, stabilizing liquid-cavity morphology, and maintaining low-loss optical feedback. Here, we report, to the best of our knowledge, the first colloidal quantum well (CQW)-based biphasic liquid microsphere laser and establish biphasic interfacial engineering as an active strategy for liquid nanocrystal lasing. Green-emitting CdSe/CdSe_1-xS_x core/crown CQWs and red-emitting CdSe/Cd_1-xZn_xS core/shell CQWs are incorporated into glycerol/toluene biphasic microspheres to construct whispering gallery mode (WGM) microlasers with chromaticity-tunable emission. The glycerol/toluene interface functions as a multifunctional regulatory boundary that stabilizes the spherical microcavity, preserves the CQW microenvironment, and provides refractive-index contrast for WGM confinement. Consequently, the green- and red-emitting CQW microsphere lasers show low-threshold, spectrally pure lasing with a linewidth of ~0.02 nm, a polarization degree of 0.923, and a quality factor up to 3.27 × 10⁴. The red-emitting device exhibits negligible decay after 800 min at 10-fold threshold pumping. Furthermore, co-confinement of red and green CQWs within a single microsphere enables continuously tunable dual-color lasing. These results establish biphasic liquid-liquid interfaces as active mediators of nanocrystal photophysics, cavity stability, and optical feedback for stable and chromaticity-tunable liquid microlasers.