$phi$ and K$^-$ mesons from Ni+Ni collisions at the beam energy of 1.91A GeV have been measured by the FOPI spectrometer, with a trigger selecting central and semi-central events amounting to 51% of the total cross section. The phase space distributions, and the total yield of K$^-$, as well as the kinetic energy distribution and the total yield of $phi$ mesons are presented. The $phi$K$^-$ ratio is found to be $0.44 pm 0.07(text{stat}) ^{+0.18}_{-0.12} (text{syst})$, meaning that about 22% of K$^-$ mesons originate from the decays of $phi$ mesons, occurring mostly in vacuum. The inverse slopes of direct kaons are up to about 15 MeV larger than the ones extracted within the one-source model, signalling that a considerable share of gap between the slopes of K$^+$ and K$^-$ could be explained by the contribution of $phi$ mesons to negative kaons.
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