In the latest flick, Phillips said Garner becomes less inclined towards his friends, Phillips Phil (Bradley Cooper), Stu (Ed Helms) and Doug (Justin Bartha), reported Contactmusic.
"To me, the key to this movie was that we wanted to tell Alan's story. It really felt like Alan's story was the loose end that needed to be tied up.
"That was the one person that we didn't know was going to be okay until we realize that he has met somebody who shares his own left-footed way that he lives. We realize that he's going to be alright and that's why it's the end. He is that loose thread," he said.
"I mean, Bradley is one of my best friends in the world now. I didn't know him before the first 'Hangover'. We've all travelled the world together, doing press and, of course, going to Bangkok. We've spent so much time together," he added.
'The Hangover Part III' will hit theatres on May 24.