We reveal the potential of step-index fibers consisting of a metaphosphate glass core and a silica cladding as an ultrafast octave-spanning supercontinuum source. The hybrid waveguide was fabricated by pressure-assisted melt filling and possesses a sophisticated dispersion behavior with two zero-dispersion points in the proximity of the Erbium laser bands. The fiber generates an octave-spanning supercontinuum from 0.7 to 2.4 μm if pumped at 1.56 μm with 30 fs pulses and energies as low as 300 pJ. Numerical simulations reveal soliton fission and double dispersive wave generation as the dominant broadening effect. This study highlights phosphate glasses as a promising new candidate for the next generation of broadband photonic devices, as they allow for high rare earth-doping levels and dispersion posttuning via plasmonic nanoparticle growth.