The integration of nanophotonic optical phased arrays (OPA) with alkali vapor cells has the potential to enhance the performance of chip-scale atomic systems by enabling novel methods for beam shaping and active alignment in atomic spectroscopy. In this work, we present the first demonstration of an OPA used for precision saturated absorption spectroscopy with a rubidium vapor cell integrated directly on the chip. The OPA, consisting of 64 emitters, expands a sub-micron waveguide mode into a >100 µm diameter free-space beam, optimized for the D 2 absorption line of rubidium. We resolved the sub-Doppler hyperfine splittings in both 85Rb and 87Rb isotopes, achieving Lorentzian linewidths ranging from 25 to 40 MHz suitable for stabilizing the cooling lasers in rubidium cold atom systems.