Microwave photonic frequency measurement with large bandwidth is of great importance in radio-frequency (RF) receiver. Meanwhile, phase identification is also an essential link for an intercept receiver. Here, we report and demonstrate a dual-functional frequency and phase measurement system with frequency measurement error of 0.12 GHz, 0.2–18 GHz measurement range, and ultrahigh phase resolution of 0.05 degree within the range of 2π. The record performance is accomplished by shifting the phase of the optical carrier within a narrow bandwidth based on stimulated Brillouin scattering (SBS), which can provide the desired frequency response through PM to IM conversion. Ultimately, the frequency/phase-to-power mapping is utilized to extract the information of the received RF signal. The results point to potential applications for satellite communications, radars, and electronic countermeasures.