With the start-up of the LHC at CERN a new era in particle physics has begun. LHCb is a precision b-physics experiment that is designed to search for the virtual effects of new particles in mixing and loop processes. One of the main goals of the experiment is to measure the CP violating phase in Bs-mixing. In this seminar the performance of the LHCb detector will be described together with the measurement of this phase in the golden Bs->J/psi phi decay mode based on 370 inverse picobarns of pp collision data. Prospects for improvements to the measurement using the full 2011 dataset in this mode, and also in the Bs->J/psi f0 and Bs->phi phi modes will be discussed.