'good phase purity' comes from wide bandwidth/high slew rate.
In order to get to 20KHz without phase shift, the upper cutoff of the circuit needs to be 10X higher, IOW 200KHz. YOu can use that as a good rule of thumb for seeing a 'fast' preamp in its specs.
Mind you, 'fast' is not the same thing as 'bright', in fact brightness is often caused by phase shift issues due to poor bandwidth. Brightness is also caused by very minimal distortion of the 5th, 7th and 9th harmonics.
In order to get to 20KHz without phase shift, the upper cutoff of the circuit needs to be 10X higher, IOW 200KHz. YOu can use that as a good rule of thumb for seeing a 'fast' preamp in its specs.
Mind you, 'fast' is not the same thing as 'bright', in fact brightness is often caused by phase shift issues due to poor bandwidth. Brightness is also caused by very minimal distortion of the 5th, 7th and 9th harmonics.