Quote:
I think speaker phase frequency response is so important for getting an idea about speakers sound and i wonder why stereophile(Mr.John Atkinson)don't measure it.

As I explain in one of my articles on measuring loudspeakers, I don't regard a flat phase response as being a major factor in determining sound quality. (See http://stereophile.com/features/100/index2.html and the following pages.) I do measure it, and in fact, it can be inferred from the step responses that I do publish.

Quote:
another important thing is output impedance of a amplifier in frequency domain(both phase and amplitude).
Is there any idea?

An amplifier having a flat response in the audioband, as 99.99% do, will not have an output impedance with anything other than 0

I agree step response in time domain refer to phase response of speakers but about amplifiers or cdplayers i think negative feedback factor is hidden in output impedance when we use two pole modeling for systems but i'm not sure.
(Vo/Vi)=G/(1-Zy)
Vo=Output voltage on the load
Vi=Input voltage
G=no load Gain of system(Vo/Vi)
Z=Output impedance of system
Y=Impedance of load
i'm not sure but i think negative feedback factor is hidden in Z.
Can you help?

This doesn't address the phase of amplifier output impedance, but in general most amplifiers will have a decreasing damping factor (higher output impedance) as frequency increases (an exception in the audio range, for instance, would be the deHavilland Aries GM70). So most amplifiers will be more susceptible to loudspeaker impedance variation as frequency increases. Tube amplifiers will of course, in general, have lower damping factors than solid state devices and will be more susceptible to loudspeaker impedance variation across the entire frequency range. The damping factor of class-D amplifiers is typically reduced a substantial amount at high frequency due to the use of a passive filter output section.

I'm not sure how much these measurements matter. There may be a host of other obscure (not often performed), candidate measurements that equally or more closely correlate with one's perception of sound quality in an amplifier.