  Using $(1.0087\pm0.0044)\times10^{10}$ $J/\psi$ events collected by the
BESIII detector at the BEPCII collider, we search for the lepton number
violation decay $\phi \to \pi^+ \pi^+ e^- e^-$ via $J/\psi\to \phi\eta$. No
signal is found and the upper limit on the branching fraction of $\phi \to
\pi^+ \pi^+ e^- e^-$ is set to be $9.7\times10^{-6}$ at the 90\% confidence
level.
