Notch filter design - resistor value
From what I know about LTSpice, and this is weird how they represent it, the dotted green line you see is the phase. So that spike in the phase line is a phase shift of \$180°\$, which usually occurs at the cutoff frequency.

The resistor value helps with your \$ Q \$ value in your curve which will affect the bandwidth of the curve.

The two blue lines must represent a DC signal since there is no change in phase or magnitude.