On the basis of a semiphenomenological model, it is argued that the anomalous properties of the bond-stretching (BS) in-plane phonon modes in cuprate superconductors and some other metallic perovskite oxides are due to coupling to the mid-infrared structure in the electronic charge fluctuation spectrum. The energy scale of this charge mode is several times larger than the phonon frequency, i.e., within 0.2-0.6 eV, and its doping and momentum dependence is discussed in relation to experimentally observed behavior of the BS phonons. Experiments on the effect of oxygen isotope substitution on the phonon softening and linewidth are suggested as a source of important information on the charge excitations, and equations describing isotope effects are derived. The set of equations is overcomplete and can therefore serve as a consistency test for the model. We discuss how the midinfrared scenario could offer an explanation of anomalous BS phonon observed in different perovskites in a unified framework.