  We present a measurement of the strong-phase difference between $D^{0}$ and
$\bar{D}^{0}\to K^{0}_{\rm S,L}K^{+}K^{-}$ decays, performed through a study of
quantum-entangled pairs of charm mesons. The measurement exploits a data sample
equivalent to an integrated luminosity of 2.93~fb$^{-1}$, collected by the
BESIII detector in $e^{+}e^{-}$ collisions corresponding to the mass of the
$\psi(3770)$ resonance. The strong-phase difference is an essential input to
the determination of the Cabibbo-Kobayashi-Maskawa (CKM) angle $\gamma/\phi_3$
through the decay $B^{-}\to DK^{-}$, where $D$ can be either a $D^{0}$ or a
$\bar{D}^{0}$ decaying to $K^{0}_{\rm S,L}K^{+}K^{-}$. This is the most precise
measurement to date of the strong-phase difference in these decays.
