https://www.theverge.com/2019/2/6/18213922/sony-xperia-xa3-phone-leak-ultra-wide-display-21-9-screen

Sony seems to be nearing the release of a phone designed for cinema buffs. New images of the Xperia XA3 posted by WinFuture reveal an ultra-wide display with a 21:9 aspect ratio. We’ve seen a wave of 18:9 smartphones in recent years, but Sony is going for an even more drastic tall and thin device. A 21:9 aspect ratio would be a match for many of today’s major films, so you'd be able to watch them on the XA3 without having to deal with black bars on the sides or at the top and bottom. But all non-cinema content would have the bars at the sides, so there's a trade-off for that immersion when streaming movies.

One nice thing about the trend of 18:9 phones (the smaller ones, anyway) is that they’re a bit easier to manage with a single hand compared to older, wider handsets. The LG G7 has a 19.5:9 display, and its one-handed usability is one of the very best things about that device. But there is definitely a point where phones can get too tall — especially if the screen itself is large. Samsung is redesigning its entire software experience around the acknowledgment that big phones are too difficult to use. Previous rumors have pointed to a 5.9-inch display, according to 9to5Google. Reaching the top of that thing sounds... rough. It’s almost starting to look like the shape of a TV remote.