Voice over LTE (VoLTE) has emerged as the mainstream voice service over cellular Long Term Evolution (LTE) network. It is observed that this VoLTE service often gets blocked during call initiation or during handoff due to insufficient radio resources. In this regard, we have presented a Physical Resource Block (PRB) based Markovian model to estimate VoLTE call blocking in cellular LTE network. Using this model we have investigated the impact of different modulation and coding schemes on call blocking in cellular LTE network providing VoLTE service.