As for the Phantom, it's strange that you attacked the 2nd or 3rd hero (I think it was an archer) and didn't go down into the mine? How did you even play like that? Before the mine, the neutrals aren't that difficult, and the map is cleared before/after the first Necromancer very quickly.
I saw the Witch before the battle with the second Necromancer; she offered Herbalism and Summoning. I saved the Herbalism spell, and for Summoning, I thought it was useless; why would I need it without the Phantom?
A little later, I went down into the mine (dungeon), saw the Phantom there, next to the mine, quickly returned, and picked up the Summoning spell. The distance was 1-2 turns without logistics.
P.S., someone in the thread mentioned (though not immediately) that the Phantom is definitely in the dungeon behind the mine.