Calculate the phase angle
In the first example, it is clear that the reference for the phase calculation is the blue trace so that Δt is measured from the blue trace zero crossing to the black trace zero crossing which is positive. In the second example, Δt is not shown so the reference trace is not clear.  I would assume, in this case, that the red trace is the reference and Δt id measured from the red zero crossing to the dotted trace zero crossing which is negative.