Measurements of the CP violating phase ${\varphi }_s$ at LHCb

The measurement of the mixing-induced CP-violating phase ${\varphi }_s$ in the $B_s^0-{\bar{B}}_s^0$ system is one of the key goals of the LHCb experiment, and provides an excellent opportunity to search for New Physics beyond Standard Model. Using Run-I data, ${\varphi }_s$ has been measured in several decay channels. These proceedings briefly summarise the previous LHCb Run-I results of ${\varphi }_s$ measurement, and show the most recent results obtained by analysing the decay channel $B_s^0\to J\mathrm{/}\psi K^{+}{K}^{-}$ in the $K^{+}{K}^{-}$ mass region above the $\varphi$(1020) resonance.