These are the Christmas trees at my job. The first picture is just a quick shot without focusing, the second is a shot I allowed the camera to focus. The flash fired when I allowed it focus. The focused shot with the flash is a true representation of what it really looks like.
That's called "lens flare" and is tricky to account for even with mid-range DSLR lenses. My best advice is to make sure the lens on the back of the Nexus is as clean and smudge/smear free as possible. if you want to do whatever is possible at your end to mitigate the flare.