Green dots while clicking photos at night

That is VERY normal and it is indeed lens flare. If you looked at your screen before you took the photo, the flare would be plainly obvious. You can diminish and in many cases eliminate the flares of bright lights reflecting off the sensor by angling your camera different relative to the scene you are photographing. There is nothing wrong with your phone. Even my very expensive Nikon DSLR will capture lens flare when photographing bright lights at night.

Here is an iPhone example I like to show.

This photo shows green dots (flares) above the lights on the outside deck:

Without changing my position, but just angling the camera differently, I was able to take the same photo without lens flare:

Does this light pixels appear on every photo on the same spot same size? If no read the Wiki article below. If yes then clean your camera surface and if that does not resolve the issue then Contact Apple for support and service - Apple Support 

Lens flare refers to a phenomenon wherein light is scattered or flared in a lens system, often in response to a bright light, producing a sometimes undesirable artifact within the image. This happens through light scattered by the imaging mechanism itself, for example through internal reflection and scattering from material imperfections in the lens. Lenses with large numbers of elements such as zooms tend to exhibit greater lens flare, as they contain a relatively large number of interfaces at which internal scattering may occur. These mechanisms differ from the focused image generation mechanism, which depends on rays from the refraction of light from the subject itself.

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It is NOT a problem. It is a normal photographic artifact and if you read what I posted, you could have diminished the flares by changing the angle of the camera. But what you tried to photograph is VERY VERY difficult to avoid lens flare.