There is no consistent standard possible when you believe morality is subjective. That's what subjective means, "up to individual determination".

That's not true. Morality doesn't have to be objective for you to be consistent with the commonly accepted subjective moral interpretation.

You think it's moral to not kill. Some communists think it's moral to kill rich people. The morality here is not objective. But you can agree that one particular variant of these subjective moralities can be dominant in your society.

It seems to me that if there is some philosophical grounding for an ethic, then that has to be objective, and so any morality with philosophy as a basis would also by nature be objective.

Okay, the ethnic I just gave you above. This is literally how morality and ethics works, so it isn't possible for you to have an objective morality.