That is a type of lens flare. Its the sun reflecting off the internal lens/ glass surfaces of the camera. I love your shots, that should be easily edited out in post. This happens sometimes even with the finest SLR lenses. Question though, did you notice it on your phone when you took the picture?
How you can tell is that its opposite of the sun. The clouds were shading the sun on top, the green dot is shaded below. If the sun is on the right, the dot is on the left, etc etc.