Carlton Reid, writing for Wired:

The use of Apple smartphones as the principal camera system on 28 Years Later was subsequently confirmed to Wired by several people connected with the movie, detailing that the particular model used to shoot was the iPhone 15 Pro Max. [...]

Several arthouse films have been shot with iPhones, including Sean Baker’s Tangerine (2015) and the Steven Soderbergh drama Unsane (2018), but these movies were limited-release, low-budget offerings compared to 28 Years Later. The new film’s $75 million budget is only part of the franchise’s total, with 28 Years Later being the first of a new trilogy; all three coming zombie films are being scripted by screenwriter Alex Garland, who is reuniting with Boyle and Mantle after helming Civil War, released earlier this year.

Right there, in your pocket, all day every day.