The branching fraction of the rare $B^0_srightarrowphimu^+mu^-$ decay is measured using data collected by the LHCb experiment at center-of-mass energies of $7$, $8$ and $13,rm{TeV}$, corresponding to an integrated luminosity of $9,{rm fb}^{-1}$. The branching fraction is reported in intervals of $q^2$, the square of the dimuon invariant mass. In the $q^2$ region between $1.1$ and $6.0,{rm Gekern -0.1em V}^2!/c^4$, the measurement is found to lie $3.6$ standard deviations below a Standard Model prediction based on a combination of Light Cone Sum Rule and Lattice QCD calculations. In addition, the first observation of the rare $B^0_srightarrow f_2^prime(1525)mu^+mu^-$ decay is reported with a statistical significance of nine standard deviations and its branching fraction is determined.
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