Recent theoretical studies have suggested that Kitaev physics and such effects as formation of a mysterious spin-liquid state can be expected not only in α-RuCl3 and iridates, but also in conventional 3d transition metal compounds. Using dc and ac magnetometry, thermodynamic, and Na23 nuclear magnetic resonance (NMR) measurements we studied such a candidate material Na3Co2SbO6. A full phase diagram of Na3Co2SbO6 in a wide range of magnetic fields and temperatures is presented. The results demonstrate transformation of the antiferromagnetic structure under the external magnetic field, gradual development of the saturation phase, as well as evidence of gapped behavior in certain parts of the phase diagram. © 2023 American Physical Society.