This work investigates the phase difference between co- and cross-polarized multipath components (MPC), in the context of the radio channel modeling of a backscattering based RFID system. The analysis is based on a measurement campaign carried out in a variety of indoor environments over the 2-6 GHz band. The phase difference between the polarization components follows approximately a uniform distribution over ]-180,180[. The agreement between the theoretical and the experimental distribution is confirmed