Phase matching between any two microphones: ?15? (100Hz to 20kHz)
I assume the unit of measure for that value is degrees, meaning the phase response of the pair is matched to within a 15 degree total tolerance difference range between 100Hz and 20kHz.
Perhaps DSatz will reply and bring us all up to speed on the implications. I'm interested myself. Until then here is my speculation-
It's relatively common to measure both frequency response and phase responses when determining a match between microphone pairs, but I don't know of other manufacturers who commonly specify that as a standard deviation specification for their pressure gradient microphones intended for music recording. It is a common specification for measurement omnis which used in sound intensity probes, since that difference needs to be corrected for to get an accurate intensity measurement. And it may also be common to do so for pressure gradient microphones intended for measurement purposes. That DPA includes that specification for a microphone intended for music recording rather than measurement purposes may be rooted in DPAs history as an outgrowth from B&K who specialize in acoustic measurement equipment and microphones.
In any case, within 15 degrees is a sufficiently close phase match such that you needn't be concerned about it for our purposes. I suspect that degree of difference to be inconsequential using typical near-spaced stereo microphone configurations (which will produce ever increasing phase-differences as the frequency in question becomes higher), and perhaps only a potential
implication for fully coincident arrangements (if the match was worse). But again, it probably doesn't matter much for music recording.