High-quality single crystals of , which resembles a perfect triangular-lattice antiferromagnet without intrinsic disorder, are investigated by magnetization and specific heat, as well as the local probe techniques nuclear magnetic resonance (NMR) and electron spin resonance. The low-field measurements confirm the absence of any spin freezing or long-range magnetic order down to 50 mK, which suggests a quantum spin liquid ground (QSL) state with gapless excitations. Instability of the QSL state is observed upon applying magnetic fields. For the direction, a field-induced magnetic phase transition is observed above 2 T from the data, agreeing with a clear plateau of , which is associated with an up-up-down spin arrangement. For the direction, a field-induced transition could be evidenced at a much higher field range (9–21 T). The NMR measurements provide microscopic evidence of field-induced ordering for both directions. A reentrant behavior of , originating from the thermal and quantum spin fluctuations, is observed for both directions. The anisotropic exchange interactions  K and  K are extracted from the modified bond-dependent XXZ model for the spin- triangular-lattice antiferromagnet. The absence of magnetic long-range order at zero fields is assigned to the effect of strong bond frustration, arising from the complex spin-orbit entangled ground state. Finally, we derive the highly anisotropic magnetic phase diagram, which is discussed in comparison with the existing theoretical models for spin- triangular-lattice antiferromagnets.