The capture is nice, however there are a few issues, the most obvious is that the highlights is to high.
Next issue is a color balance issue. The image is slightly blue. You need to add some warmth.
There are two others that are less obvious; that you will need to zoom to between 100 and 200% to see.
The color between the stone is not smooth. There are signs of both luminance and chromatic noise.
Also especially near to the flowers, there is color fringing on the edge of the stones.
Was this rejected because of image quality?
Because you have taken this with a smartphone, there will be issues with image quality. The sensor size is small in smartphones, so therefore detail is lost when enlarged. In your photo, when zoomed in, the pixels become smooth due to the phone's processing of the photo. See here:
Also as mentioned, the image is a little blue, and the sky is too washed out. This is because you are shooting into the light and that it's an overcast day. The composition is not so good either.