Axis & Allies Developer and Playtester; War of the Ring Editor and Playtester
Re: During which game trun phase may you use the ability of a Companion or Minion?
They are all used during the Action phase. When the players take turns executing the Actions allowed by the Action Dice.
Some Companions' Guide abilities can also be used during the Fellowship Phase, in the relatively rare event that a Hunt tile is drawn upon declaration of the Fellowship due to certain abilities and events.