Here I am, teaching evolution to a creationist even though I consider it an indulgent waste of time. Can't be any worse than video games, I guess.
It's hard to tell what you're tying to say, because taken at face value your words make no sense. Phylogeny is the study of the evolutionary history of a species. Taxonomy is the system by which different organisms are classified. Phylogeny is a useful tool for taxonomists, not an alternative system developed to accommodate some "barrier."
Did you mean that there is a physical barrier beyond which a species cannot possibly evolve? Take modern wolves, for example. Are you saying they could never, in any number of generations, evolve into something you wouldn't recognize as the same species? If so, where is your evidence? Remember, even if no one directly watched it happen, that's not evidence that it's impossible, which is the argument you're making.
Oh, there's all kinds of interspecies copulation. You've clearly never been on a farm
But I think you meant that animals generally only
reproduce within their own species, and that's true enough for the most part. That's no surprise seeing as that's part of the definition of "species."
But that's neither here nor there. No one is suggesting that evolution happens via cross-species interbreeding. Evolution happens on the population-level, not the individual level. Evolution occurs when certain traits are favored by environmental pressures and others aren't. When the environment changes, so do the traits expressed in the population. After enough changes in the environment happen, the population can have changed so dramatically that they are no longer reproductively compatible (cannot mate or produce fertile offspring) with members of the species from which they originated. This is called speciation, and it's been observed directly in rapidly-reproducing populations like fruit flies. It takes much longer for a population to evolve so dramatically that it requires a brand new genus to be named for it, but there's no evidence suggesting that it can't happen. There's no evidence suggesting that it can't happen past any taxonomic level, in fact. I know that's your main objection, that evolution cannot occur past the genus level, so I await your evidence supporting that. And do keep in mind what counts and what doesn't count as evidence.