In a wide range of quantum technology applications, ranging from atomic clocks to the creation of ultracold samples for atom interferometry, optimal laser sources are critical. In particular, two phase-locked laser sources with a precise difference frequency are needed for efficient coherent population trapping (CPT) clocks, gray molasses laser cooling, or driving Raman transitions. Here we show how a simple cost-effective laser diode can selectively amplify only one sideband of a fiber-electrooptically-modulated seed laser to produce moderate-power phase-locked light with sub-Hz relative linewidth and tunable difference frequencies up to ≈ 15 GHz. The architecture is readily scalable to multiple phase-locked lasers and could conceivably be used for future on-chip compact laser systems for quantum technologies.