Look at the entire photo, and it's easy to see the photo was taken at a slight angle. The bottom of OP's phone is closer to the lens than the top is, which makes the bottom of the phone appear larger in the image than the top, which means all parts of the phone (including the bezel) will appear slightly larger on the bottom of the photo than at the top.
To confirm this you can see the sides of the phone are not perfectly parallel with the sides of the photo. This is known as keystone distortion in photography, and it's why (as an extreme example) we see the tops of buildings as smaller than the ground floor when we take photos.
With keystone distortion there is no size difference between objects in the top and bottom of the frame, but the greater distance of the object at the top of the frame (in this case, the top of OP's phone) makes it appear slightly smaller. So we cannot know for sure that the top bezel is thinner than the bottom one, due to how the photo was taken.