Why is phase noise important?
Phase noise is not typically a term that applies to op amps. Phase noise usually refers to precision frequency synthesizers and clocks. If a clock has phase noise, that means the clock transitions are not at exactly the same point from cycle to cycle, even if the frequency is constant. This matters when the clocks drive data converters because they will not sample the incoming signal at exactly the same point on each cycle, which leads to increased noise and distortion. The relevant term for op amps is phase margin, which describes how much room is left before the op amp output is 180 degrees out of phase with the input, which will lead to oscillation.