Summary form only given. In this paper, the phase error in the MSK (minimum shift keying) receiver carrier and crosstalk between the I and Q channels are assumed. Also, the phase error is a random variable due to noise and other random input processes. Here, besides this imperfect carrier extraction, interference due to communication channel features is assumed. Since the interference can be the consequence of different events, the interference phase has uniform distribution. The influence of the imperfect reference signal extraction is expressed by the probability density function of the first order PLL (phase locked loop) phase error. The distribution parameters depend on the PLL structure, the equivalent noise bandwidth of the loop, the loop gain, the useful signal as well as the interference at the receiver input. For the presentation of this problem, the error rate, as a measure of the quality of the digital system, is calculated numerically and the detailed analysis of the obtained results is performed.