Quote from peteroupc »Nothing happens "between" steps or phases. In general, a step or phase, including the main phase, ends only if all players pass while the stack is empty (C.R. 500.2).
Also, by saying you will move to combat, you are merely proposing a shortcut that any other player can shorten. For example, after you say "move to combat" during your main phase, your opponent can shorten it by casting an instant spell during that same main phase. If they do, and assuming this is a two-player game, the instant is cast and the game will still be in your main phase.
Quote from tvalli90 »So once I cast my last spell for the phase, all players have a chance to respond to the phase ending. So I can say, "Move to Combat". But that would not prevent other players from casting a spell at the end of main 1. They still the opportunity, and I can't circumvent that by just saying, "Move to combat".
Quote from Rezzahan »Also note, that since your shortcut was not accepted, you are not bound to keep from playing more stuff in the same step/phase. The game is still in your first main phase, even after your opponent's spell/ability has resolved. So you could then still play a creature for example in the precombat main phase afterwards.