In the recent years, measurements of rare B decays involving b->sll transitions have shown discrepancies compared to predictions of the Standard Model of Particle Physics. These transitions are flavor-changing neutral currents (FCNC): they are forbidden at tree level in the SM and therefore sensitive to contributions of new particles in loops. Global fits to these data suggest new physics contributions that can be explained new physics models involving a tree-level exchange of a lepto-quark or a flavor changing $Z^\prime$ boson. In the decay of neutral Bs meson to a CP eigenstate, the interference between the decay and the B-meson mixing leads to additional observables that are not accessible to flavor specific final states. In the SM, all CP-violating effects are expected to be very small, therefore these observables can make powerful contributions to our understanding of the B-anomalies as they can differ significantly depending on the properties of new physics contributions. This project will measureme the CP violating observables arising in the interference of the decay and mixing of Bs mesons using a tagged analysis for the first time in phimumu decays using full LHCb data set which corresponds to 9 inverse-fb. Additionally a new method to calibrate decay time resolution at LHCb will be developed and tested on run 1-2 data collected at LHCb and will be ready to use for the run 3 which is expected to start at the end of 2021.