Do blocking creatures heal back to full between phases?
It will be destroyed. All damage done to the creature in most cases stays until the very end of the turn (cleanup step).


  119.6. Damage marked on a creature remains until the cleanup step, even if that permanent stops being a creature. If the total damage marked on a creature is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed as a state-based action (see rule 704). All damage marked on a permanent is removed when it regenerates (see rule 701.12, “Regenerate”) and during the cleanup step (see rule 514.2).