  Quantum random number generator (QRNG) utilizes the intrinsic randomness of
quantum systems to generate completely unpredictable and genuine random
numbers, finding wide applications across many fields. QRNGs relying on the
phase noise of a laser have attracted considerable attention due to their
straightforward system architecture and high random number generation rates.
However, traditional phase noise QRNGs suffer from a 50\% loss of quantum
entropy during the randomness extraction process. In this paper, we propose a
phase-reconstruction quantum random number generation scheme, in which the
phase noise of a laser is reconstructed by simultaneously measuring the
orthogonal quadratures of the light field using balanced detectors. This
enables direct discretization of uniform phase noise, and the min-entropy can
achieve a value of 1. Furthermore, our approach exhibits inherent robustness
against the classical phase fluctuations of the unbalanced interferometer,
eliminating the need for active compensation. Finally, we conducted
experimental validation using commercial optical hybrid and balanced detectors,
achieving a random number generation rate of 1.96 Gbps at a sampling rate of
200 MSa/s.
