Wouldnt that depend also partly on how fast the phase changed? For example, if the phase changes slowly that's a low frequency component, and if it changed fast then that would be a high frequency component.
Narrow band FM is generally considered to be where this is only single set of significant sidebands. This makes it similar in bandwidth to an AM signal.
Modulation beta index of about 0.6 if I recall.
Refer to Bessel function for carrier and sideband level.
beta (delta F / freq of modulation)