Highly nonlinear photonic crystal fibers have the characteristics of small core and large refractive index contrast. Due to its periodic air hole structure, the phonons generated by the guided acoustic-wave Brillouin scattering (GAWBS) are tightly trapped in the core area and interact significantly with photons. The refractive index of the fiber will be modulated by phonons, resulting in a phase modulation on optical waves. Using the Sagnac interferometry to transform phase modulation to intensity modulation, we demonstrate the generation and detection of phonons by GAWBS in the photonic crystal fiber in the 1550 nm and 1060 nm bands, respectively. The experimental results show that the fundamental mode frequency of acoustic phonons is 1.24 GHz for both cases with the pump wavelengths of 1550 nm and 1060 nm, respectively, which verifies the theory that the phonon frequency in forward Brillouin scattering is independent of the pump wavelength.