Determination of the phase $\phi_{s}$ at LHCb

The determination of the mixing-induced $C\!P$-violating phase $\phi_{s}$ in the $B^{0}_{s}-\bar{B}^{0}_{s}$ system is one of the key goals of the LHCb experiment. Using several $B^{0}_{s}$ decay modes it has been measured by the LHCb collaboration exploiting the Run I data set. The first observation of the $B^{0}_{s}\to\eta_{c}\phi$ and $B^{0}_{s}\to\eta_{c}\pi^{+}\pi^{-}$ decay modes which can be used to measure $\phi_{s}$ with Run II data is presented.