Various P2 and P'3-NaxCoO2 phases, with x ranging approximately from 0.6 to 0.75, have been studied by variable-temperature Na-23 magic angle spinning (MAS) NMR. Signal modification versus temperature plots clearly show that Na+ ions are not totally mobile at room temperature on the NMR time scale. As the temperature increases, the line shape change of the Na-23 MAS NMR signal differs for the P2 and P'3 stackings and is interpreted by the differences of Na+ ion sites and of sodium diffusion pathways in the two structures.