The 71-year-old director talked about the experience Thursday night at a Tribeca Film Festival screening of the movie, which was followed by a panel discussion that included cast members Liam Neeson, Ben Kingsley, Caroline Goodall and Embeth Davidtz.
"Robin knew what I was going through," Spielberg said of Williams, adding the comedy icon called him once a week to lift his spirits.
"He knew exactly what time it was in Poland... and he would do 15 minutes of stand-up on the phone and I would laugh hysterically because I had to release so much," Spielberg said. "The way Robin was on the telephone, he would always hang up on you on the loudest, best laugh he'd give you. Drop the mic. That's it. Never said goodbye. Just hung up on the biggest laugh."
Williams starred in dozens of movies, including Spielberg's 1991 fantasy flick Hook. He won the Oscar for Best Supporting Actor in 1997's Good Will Hunting, but his career was cut tragically short when he hanged himself in his California home in 2014 after suffering from Diffuse Lewy body disease, a form of dementia. He was 63.