A phase-domain delta-sigma (ΔΣ) modulator in a phase digitizer determines a demodulated phase error based on a phase-modulated frequency signal, in which a carrier frequency is modulated with a fundamental frequency and an associated phase, and a selected one of a set of reference signals, where the demodulated phase error represents a difference between the phase and a reference phase of the selected one of the set of reference signals. Moreover, a digital filter in the phase-domain ΔΣ modulator filters the demodulated phase error. Furthermore, a latch in the phase-domain ΔΣ modulator provides a bit stream by sampling one or more bits of the filtered demodulated phase error, where an average value of the bit stream represents the phase. Next, control logic in the phase-domain ΔΣ modulator selects the one of the set of reference signals.