How do you know if the phone doesn’t have an appropriate focal length if the image isn’t marked?

Secondly, none of the points in the article are about optical distortion across the lens they’re all about perspective distortion. Corrective elements aren’t going to change that. None of the examples highlight barrel/pincushion distortion or the like as an offender.

> How do you know if the phone doesn’t have an appropriate focal length if the image isn’t marked?

I listed focal lengths for an iPhone 16 Pro Max, and good focal lengths for flattering portrait photography is common photography knowledge that I provided as well for reference, set with a little wiggle-room by the optics of the human eye.

There aren't more variables than subject framing and focal length, and a portrait of a person is a well-known size. Comparing the remaining two numbers is simple math.

(It is well-known what distortion effect using the "wrong" focal length will give, which can sometimes be used intentionally but is not what you want in the average portrait. Shorter focal lengths give a silly, elongated facial appearance which exaggerates frontal features like nose and mouth, longer focal lengths give a flatter appearance which exaggerates rear features like neck width.)

> Secondly, none of the points in the article

The article clearly shows distorted images, and that the article fails to mention it does not make it less of an issue.