Why do iPhone photos of myself stink, but flash looks good?

Whoever I take a pic of myself in the day, I think it looks awful. There are shadows under my eyes and my cheeks look puffy. It also seems like you can't get too far away from the camera. At night with flash, it looks great! Is it better to just use a regular camera for day pics?

This is because you have not yet learned the fundamentals of lighting. Full sun will always produce harsh shadows on a person's face unless the sun is placed somewhere behind the subject.

If you use the mobiles flash as flash fill this can remedy the problem or if you have something to reflect the sun into your face, those shadows will be reduced, however, selfies are still going to distort your facial features since a mobile has a fixed wide angle lens (your puffy cheeks)

So, the answer is, you need to learn some basics when it comes to photography, lighting and composition before you can expect your images, taken with a mobile to look better than everyone else's

Good advice there from fhotoace…
You can also set your iPhone to fire the flash every time and this will give you a 'fill flash' that beats the shadows in high contrast sunlight.
You could also put one of these fold up reflector in your bag and have someone hold it to reflect shadow-lightning daylight back at you.

https://www.bhphotovideo.com/..._disc.html

Bad lighting.

Set the camera up farther away from yourself (in the daytime)
and see what happens.

It is not just the camera alone. What matters most is the skill of the photographer.

The shadows under your eyes presumably come from using the camera in unsuitable lighting conditions. If you use flash the whole face is illuminated evenly, but there's the risk of red eye. Indeed holding the camera yourself just two or three feet from your face gives distortion of your face - the nose shows too big. Have the camera at least 5 feet (1.5 metres) from your face.

Try using the camera without flash, but in lighting which is even and diffuse from the front. Maybe under a tree without direct sun, or in a room with a big window but without direct sun coming through the window.

I suspect you don't know much about lighting; it's one key feature in photography, an important part of the very basic fundamentals of photography. And it's so easy to learn… (check Youtube.com for tips on portraits with a cell 'phone camera).

Without the flash you're relying on the overhead light directed downward, that casts a shadow beneath certain areas of your face (and body). The flash is directional, and highlights your subject (yourself) you point your camera at, so it's understandable that it lights areas that would otherwise have shadows from overhead light because of the direction of the light from the flash.

Now, if you were to take a photo of yourself during an overcast day, you'd find that the clouds scatter the light from above (the sun would be hidden above the clouds); the sun's light filters through and it is diffused, or scattered, thusly not causing shadows. The very worst time of the day to take a photo (whether with a cell 'phone camera, a point-and-shoot, bridge camera or DSLR) is at noon or close to noon on a very bright, sunny day. You'd do better taking photos very early in the morning or very late in the afternoon when the sun is low in the horizon and the sunlight is coming from one side of your shoulders, but not in front (or you or your subjects may have to squint) or if the sunlight is coming from behind you or the subject, the result in the images may show a shadowy or very dark face with light glare coming from behind you or your subject(s).

Here's a trick you can use and it won't cost you a penny. Cut out a piece of frosted white plastic from the side of an empty plastic container, the size of a credit card will do nicely, and you can store it in your wallet or your shirt pocket with your cell 'phone. When you're using a flash (on your cell 'phone, point-and-shoot or bridge or DSLR) and your subject is close, put the piece of frosted plastic in front of the flash area! It will diffuse the light and prevent flash eye-sting (never look at the camera; always look slightly at the top of photographer's head, this also prevents red-eye effect). TRY it at home and practice (you can always delete it, yes or YES?) And you can also carry a small rubber band so you can hold the plastic temporarily on your cell 'phone so you won't have to hand hold it.

Taking "selfies" only gives you one other problem, the very tiny, very wide angle lens causes distortions, making your features seem pulled forward (elongated toward the lens) and your other parts (ears, shoulders seem smaller, called wide angle perspective or wide angle distortion) because your arms are simply not long enough; the better distance would be about 5 to 6 feet away to avoid wide angle lens perspective/distortion.

Easy, the reason is bad photographer. The person taking the shots is doing so under bad lighting which makes subjects look bad and unattractive. Choose better light, and your photos will almost always look better.