  Based on $(448.1 \pm 2.9 )\times 10^6$ $\psi(3686)$ events collected with the
BESIII detector operating at the BEPCII collider, the decay
$\psi(3686)\rightarrow \phi K_{S}^{0} K_{S}^{0}$ is observed for the first
time. Taking the interference between $\psi(3686)$ decay and continuum
production into account, the branching fraction of this decay is measured to be
$\mathcal{B}(\psi(3686)\rightarrow\phi K_S^0 K_S^0 )$ = $(3.53 $ $\pm$ $0.20$
$\pm$ $0.21$)$\times 10^{-5}$, where the first uncertainty is statistical and
the second is systematic. Combining with the world average value for ${\mathcal
B}(J/\psi\to \phi K^0_SK^0_S)$, the ratio $\mathcal{B}(\psi(3686)\rightarrow
\phi K_{S}^{0} K_{S}^{0})/\mathcal{B}(J/\psi\rightarrow \phi K_{S}^{0}
K_{S}^{0}) $ is determined to be $(6.0\pm 1.6)$%, which is suppressed relative
to the 12% rule.
