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This paper presents a 4-b phase-domain analog-to-digital converter (ADC) that utilizes the time-domain reference generation scheme for low-power operation. Rather than prior arts that rely on power-hungry resistive/current combiners or the IQ-assisted binary-search algorithm with large power T&H circuits for the reference generation, this design benefits from the fully dynamic power characteristic of the time-domain operation, thus leading to an energy-efficient phase ADC design. By introducing several on-chip calibration techniques, the design achieves good robustness with the proposed time-domain operation. The prototype is fabricated in the standard 65-nm CMOS technology, achieving an ENOB of 3.42 bits at 1 MS/s with near Nyquist input, while dissipating $7~\mu \text{W}$ from a 1-V supply. It leads to a 1.36-pJ/conversion-step Walden Figure of Merit at Nyquist input (FoM@Nyquist).