There's a lot of vocal stacking used at 2:25. Many vocal harmonies are layered below the Lead vocal. To create these kind of harmonies you can use "Melodyne" for example and change the melody of the vocal (you need to know about chords and harmonies though). Another way is to use a harmonizer VST (e.g. Eventide Harmonizer). If you just wanna have the same vocal "duplicated" you can use Chorus or Doubler Effects (check out Waves Doubler). But you won't get the same results as if you had recorded several original Dubs for the Lead Vocal.
Moreover it seems to me that some of the backing vocals in the track were recorded in a live room with a mic in the mid (atleast it sounds really authentic).