Rosamund Pike called out an audience member for texting during an emotional moment from her performance in West End play Inter Alia on Saturday, saying: "When I feel that and see it, it's hard."
The actor and producer returned to the stage at the end of the play at Wyndham's Theatre to politely remind people of theatre etiquette.
Pike said she hoped the guilty texter was a doctor and that their message had been "very important", during an impromptu speech which drew gasps and then cheers.
"I just wanted to say for anyone going to the theatre, it's a huge thing that we're trying to give you. I am trying to tell you a story, and I'm feeling you, and I hope you're feeling me too," said the Saltburn and Gone Girl star.
Earlier this year, the actress won the Olivier Award for best actress for her role as Jessica Parks, a London Crown Court judge balancing work and family life.
The play, written by Olivier Award-winning writer Suzie Miller, focuses on sexual assault and the injustices of the legal system.
Pike - who also asked the audience not to film her speech - addressed a certain broad section of the stalls which had distracted her during a crucial scene.
"You know who you are and I'm not going to single you out," she said.
"Maybe it was very important, and maybe you're a doctor, and you're saving someone's life, and I hope you are, but we do see these, we do feel them.
"I've got you, I feel like I've got to hold you all, so when I feel that and see it, it's hard."
The audience gasped during the speech and were "irritated and annoyed" that someone had been on their phone, before cheering and applauding when the speech was over, the BBC understands.
An audience member who witnessed Pike's speech, and who wished to remain anonymous, applauded the actress for her intervention.
She told BBC News: "At the end of Inter Alia, an incredibly moving and thought-provoking play, Rosamund Pike came back on stage alone.
"I assumed she would announce a charity collection, as is common in West End shows. But we were stunned to hear her berate an audience member in the front of the stalls who had been texting throughout the final, most moving scene.
"The audience was suitably appalled, although next to us a gentleman had an Apple Watch going off constantly and the couple behind me talked through the whole show."
The section when the person was on their phone was "the hardest bit of the play" where a serious admission is made on stage, the audience member told us.
She added: "I wholeheartedly applaud Rosamund for her speech, where she didn't directly identify the person, but did explain at length the impact on an actor if someone is on their phone. Sadly, I doubt this person will feel any guilt as we live in such an entitled world now."
Addressing the debate around phones in theatres more broadly, she said she was still "totally behind audiences filming the bows", however, and supported the idea that people should be able to capture curtain calls.
She pointed out that many shows already film and share the bows online - and for parents of child actors it may be "the only footage they'll ever have of their children on a West End stage".
But, she said, there is "absolutely no excuse for a phone during a show" as "in an emergency you can simply leave the auditorium to deal with the issue".
Pike is not the only actor to have called out audience members for using their phones in the theatre.
Other stars including Daniel Craig, Hugh Jackman and Patti LuPone have all made similar comments, while Lesley Manville told BBC Radio 4 last month that she found it "insulting" when punters took photos of curtain calls, even.
Manville, who received an Oscar nomination for her role in the 2017 film Phantom Thread, said people should "take the digital out of it for just a moment".
"Come on, it's theatre - let's preserve it!" she added.
"We are all in this room, we are telling you a story, you're listening - clap or don't clap, but don't just stick your phone in our face. I find it insulting."
Speaking to BBC Radio 4's World at One on Monday, actress Juliet Stevenson praised Pike's actions, underlining how actors and audiences share a mutual "responsibility" in maintaining the "illusion" of an "imaginative world".
She argued that "one person's phone going off shatters that for everybody" and so disrupting the experience is "an act of extreme selfishness".
"It's very difficult for the actor because you feel not only is your own concentration very disturbed and you're pulled out of the fiction, but then you also feel you've got to try and pull the audience back as well, so you've got kind of two responsibilities."
