Phase lag is governed by Lock number which is a ratio between blade inertia and aerodynamic damping..
This is not correct. The Lock number has very little to do with it.
The critical parameter for the phase shift is the relative flapping hinge offset. This is the ratio between the distance of the flapping hinge from the rotor axis and the blade tip radius. (or the virtual hinge location for a flexbeam rotor).
Due to this distance you get bending moment that tilts the whole helicopter including its rotor shaft axis. This happens at an phase angle smaller than 90° (0° phase angle for a totally rigid rotor with a relative hinge offset equal to 1).
You still have the gyroscopic effect with 90° phase shift for the tilt of the roation axis of the rotor blades (which is then generally not parallel to the rotor shaft axis). The combination of these to tilting effects results in a total tilt at an intermediate phase angle.