What is the mm on the iPhone 6 Plus front and back camera?

Since you're alluding to your selfies looking distorted, this is more of a distance from camera to subject issue. When taking pictures at such a close distance you will get perspective distortion. Think of taking a closeup picture of a dog's nose. That's what you are doing to yourself, creating a dog nose photo which looks silly.

The cure is to take selfies with the camera at least 5 feet away, or at least use a selfie stick to get the camera farther away. If you continue to take shots at arms length, you will look silly.

A phone camera is really good for fender benders. If you want an honest result of a human being you want a camera with at least a 18-70mm lens. The 70mm end will give you the proper persective to render a human "normal" looking.

Wide angle at arm's length is severely distorted. Let someone else take your picture using a real camera.

Yes, the wide angle lens will distort anything that is relatively close to the lens, like arm's length. The more you back away from the lens, the less noticeable the distortion.

It's around 4 or 5mm which converts to about 28mm in 35mm format. Yes, this is very wide and will produce a great amount of wide-angle distortion.