Historical Rules · 5 February 2021
Rule 505.1a
Official source text from the 5 February 2021 Rules release
Only the first main phase of the turn is a precombat main phase. All other main phases are postcombat main phases. This includes the second main phase of a turn in which the combat phase has been skipped. It is also true of a turn in which an effect has caused an additional combat phase and an additional main phase to be created.