Our phones have something called autoexposure, meaning it automatically dials in the settings to expose the image correctly. What your phone does is that is looks at the image and averages all pixels and then it exposes for that average meaning that the moon if brighter than the sky will look like a white blob. Our eyes however expose for the brightest part of our “image field” giving us the details of the moon.
There is also a problem with resolution and noice. The phones camera sensor is quite small and pixel dense, this can lead to images being noisy. If the thing you are trying to photograph is small, you will probably zoom in but if your phone doesn’t have several lenses or some kind of zoom lens (highly unlikely) this won’t make a difference, it will simply crop the image beforehand making the noice more noticeable.
TLDR: There are many factors, leading ones are wrong exposure, “bad” optics and sensor size.
Edit: Made some corrections and formatted a bit.
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