Photonic crystal fibers (PCFs) constitute a new class of optical sensors because of its diverse advantages. Large possibilities of tailoring different parameters and sensing properties of PCFs by means of geometry design are very promising and are extensively investigated. One of research fields of the PCF are interferometer sensors, where demodulation (processing) of an output signals needs a phase sensitivity to a measurand. We present our theoretical research of phase sensitivity of the Photonic Crystal Fibers with different geometry. In our computations, we make use of the Multipole Method for calculation of an effective refractive index of the fiber. On this basis we determined the phase changes caused by the mechanical disturbances (elongation, bending) as well as temperature changes.