There does seem to be some lack of uniformity regarding the definition of
microevolution.  However, it hardly matters, as I see it.  We apparently all
agree that new species do arise from earlier species, regardless of how we
label that reality.  In other words, a species accumulates changes over time
until finally it is different enough from the original that it only makes
sense to give it a new name.  If such a process continues long enough,
surely that series of species will become different enough from the original
that it would have to be classified in a new genus.  It is difficult for me
to appreciate that in the overall scheme of nature, a different process is
involved in the production of new phyla or classes than is involved in the
production of new genera and families.  I thought taxonomy viewed this as a
continuum?  It is also well to keep in mind that phylum is not a concept
which nature recognizes.  Nature recognizes only diversity.  Taxonomy is our
own creation, an artificial attempt to organize nature's diversity into
something our limited minds can deal with.  We might think in terms of a
species needing a new genus, or having to be moved to a new family.  Nature
only produces ongoing change in all things, living and non-living, and
leaves the classification of such things to us.
Paul M.