In the past few years, we have covered plenty of anamorphic iPhone lenses that let you capture cinematic 2.40:1 ultra-widescreen videos. The Beastgrip Pro 1.33X Anamorphic Lens MK2 is also worth a look. It is compatible with Beastgrip Pro rigs and Beastcage for iPhone. It also has a 58mm lens mount.
This 1.33X anamorphic lens is great for capturing widescreen 2.4:1 aspect ratio footage with horizontal lens flares for a more cinematic look. The above video gives a better idea what you can do with it. With these lenses, you will need an app to de-squeeze your footage.