but how do you show that a whole new phylum can come from this?
A better question might be: what would prevent the mechanisms of evolution from creating new phyla? So far I don't think we're aware of any process that would prevent mutations and natural selection from creating any new phyla, or even kingdom.
BOTH abiogenisis and evolution are required for a natural explanation for the origin to life as we know it.
Otherwise, Who among us will say God created life from inert materials, but evolution did the rest?
You say you realize that abiogenesis and evolution are different topics, yet you posit both are required for a natural explanation for the origin of life even though evolution has nothing to do with origins. Something doesn't compute.
I think it's deists who claim that god simply set the universe up and then let everything run on its own. Why can't god just simply be the person who winds up the watch and lets it run? Certainly off-topic here, but there should be a thread somewhere within the faith forums that would cover this. If not, propose one.