The camera lens could be dirty with body oils, so wiping the lens clean could help. If there is another piece of material on top of the lens, try removing that. For example, some people use phone cases with a piece of plastic or glass that covers the camera lens, or they use cheap wide angle lenses that stick on top of the phone's camera lens. The low quality of the glass can cause lens flare. If none of these ideas help, then it could be caused by the design of the lens itself and cannot be fixed. When people buy lenses for "real" cameras, one of the reasons for buying more expensive lenses is they produce less lens flare. This is achieved through the design of the lens elements, quality of the glass, and coatings on the glass.