I can't count the number of times a simple mistake has cost me the game. Nine out of ten times its skipping attack and going straight to fortify; but there's others. Sometimes its my fault, sometimes its the game lagging while I re-tap the same spot.
During your turn, how about changing the players avatar to a back button, even if it only lasts 1-2 seconds after making a move. If you accidentally skip attack, that half a second later you can undo. It would also be great for returning to draft cards if you go to attack too quickly.
Maybe it could be used to undo troop draft real quick, or at the end of a turn for half a second in case you skip fortify.
A back button would work, but also a small sliding bar or something that has 3 (or 4) stages you can navigate - separated from the dice - Draft, attack, fortify (and maybe finish).
I like that idea better because a player cannot undo a regret move a second later. A sliding bar would just prevent the unintentional mistakes.
Enrique, in the short term you can enable the "end of phase confirmation" in the in-game settings. Not exactly what you're after, but it's an existing feature just in case.