Updated August 29, 2019: Tom Holland filmed a scene as Peter Parker for Sony Pictures' Venom but it was cut from the film by Marvel, according to Collider.
"I’ll tell you the truth: Tom Holland did film a scene for Venom," Collider's Jay Washington said on Collider Live! "Marvel saw the movie and was like 'Take this out. Take this scene out."
Washington elaborated, saying "Peter Parker was in Venom, not Spider-Man," though he didn't not specify any reasoning behind the distinction.
Back in January 2018 when Venom was being filmed, Collider's John Schnepp said that Tom Holland would appear in Venom as Spider-Man (as referenced below).
Holland himself has said that there was plans for him to voice a cameo in Sony's animated Spider-Man: Into the Spider-Verse but it was aborted.
Original Story from January 17, 2018: Tom Holland's Spider-Man will appear in this fall's Venom movie from Sony, according to Collider. In the latest episode of Collider Movie Talk, John Schnepp stated that the character would appear despite previous talk from Marvel Studios and Sony that the movie is unnconnected to the Marvel Cinematic Universe.
“Spider-Man is going to be in Venom,” Schnepp stated. “For the last couple of months, we’ve been hearing how Sony is keeping it all separated, and Spider-Man is in the Marvel Cinematic Universe, but every other character that’s in the Spider-Man universe is separate. All I’m saying is that Spider-Man - and I’m talking about Tom Holland’s Spider-Man - is going to be in Venom.”
Venom is scheduled to open in theaters October 5.