I'm Still Here was a documentary directed by his brother-in-law Casey Affleck depicting a year in the life of Phoenix, as he quits acting to become a rap artist, attacks fans and slides towards drug-induced depravity. Was it real? Was Phoenix having a breakdown? No. After 12 months of speculation, it transpired it was fake, yet another bizarre pit-stop in the anti-career of Joaquin Phoenix.
Phoenix has always come across as a troubled soul. Unsurprising, given he witnessed the death of his older actor-brother River from a drugs overdose outside LA's Viper Room club in 1993. And after playing Johnny Cash in biopic Walk The Line – an apt title for an actor who treads such a high-wire – he endured a stint in rehab after his drinking got out of hand. This time, he simply wanted to change his "approach to acting", he says. "I was bored with it. It wasn't exciting any more."
Today, sitting in a hotel ballroom in Venice, dressed in a denim shirt, navy trousers and striped braces, the actor has an almost guilty look on his face. He has a confession to make about I'm Still Here.
"I feel bad about people feeling that we were in some way trying to make a movie that was attacking them, or an industry.
"I didn't like that at all. We were really making fun of ourselves. That's all that it was. We were never going after other actors- I don't want to be combative. I don't want bad feelings."
There aren't any – not least because in spite of his oddities, the 38-year-old is one of the most talented actors of his generation. Four years after his last feature role, in James Gray's aching romance Two Lovers, his return to 'traditional' acting is a triumph. The Master is the new film by Paul Thomas Anderson, director of There Will Be Blood, a ravishing work that has seen Phoenix's performance compared to that godfather of Method acting, Montgomery Clift.
Set in 1950, he plays demobbed sailor Freddie Quell, an unhinged Second World War survivor who finds re-adjusting to civilian life impossible. Until, that is, he meets Lancaster Dodd (Philip Seymour Hoffman), a visionary or a quack depending on your viewpoint, who runs a self-help movement known as 'The Cause'. Freddie becomes both acolyte and antagonist. "I think that's what's so appealing to Freddie – Dodd genuinely seems to be interested and genuinely seems to care," says Phoenix, of the complex relationship that emerges.
Anderson had already confessed that Dodd is based on L. Ron Hubbard, the founder of the Church of Scientology, the controversial religion followed by such high-profile celebrities as Tom Cruise. For his part, Phoenix refuses to get drawn into the debate. "People find contentment or satisfaction from being Catholic, then that's awesome," he says, warily. "And if they find it with being a Scientologist, then that's awesome. Or they can find it from not being part of any group. People have the right obviously to believe what they want; it's whatever makes you happy."
Already, Phoenix and co-star Hoffman have shared the Best Actor prize at the Venice Film Festival. A third Oscar nomination for Phoenix, following his nods for the emperor in Gladiator and Walk The Line, seems a certainty. And yet if Phoenix has been revitalised by his enforced hiatus, he admits he was angst-ridden going back into the breach. "I'm nervous every time I make a movie. Of course I'm anxious about it. There was part of me that thought – 'Oh f**k, am I going back into this?'"
He blames his discomfort on growing up in that world. Born in Puerto Rico, to missionary parents, after time spent in Latin America, his family settled in Florida, where Phoenix and his four siblings were swiftly signed up to a talent agency. "I was a child actor. I started when I was eight, and everything they teach you is wrong," he says. "They say 'Learn your lines, find your light and hit your mark.' All the things you shouldn't do! It took me 30 years to realise that they were wrong – or at least for me!"
It's why his work in The Master is so uncompromising, as if he's unlearning all that's gone before. Just watch the scene where Freddie and Dodd are jailed, Phoenix reacting like a caged wild animal. Dropping 25lbs, he deliberately starved himself to keep him on edge. "I was very hungry," he nods. "We had one shot left, and I got this bag of chips, and I put it in my trailer. The moment they said, 'Cut', I ran [to the trailer] and I didn't stop eating for a week. I sent Paul pictures of my gut!"
He's been there before of course – from gaining puppy-fat for Gladiator to crash-dieting to play an environmentalist in a Malaysian prison in Return To Paradise. But those were controlled, calculated decisions; the new improved Phoenix – who has since, in a flurry of work, shot Spike Jonze's Her and James Gray's magician tale Nightingale – wants to, quite literally, act on instinct.
"I want to get to a place where I just acknowledge that I'm not stirring the ship," he smiles. He may no longer be the master of his own destiny – but that, it seems, is what excites him.
The Master opens tomorrow