iPhone 6S plus black spot in lower left

Hi all, I'm new to the community but just purchased an iPhone 6s plus. I bought the phone from Verizon about a week ago and love it. However, on the lower left hand corner there is a small black (shaded) spot. It's about a half inch from the bottom left corner. Since I'm within the 14 day period, I had Verizon send me another phone, but the new phone was even worse than the original. Today I went into the Apple store and they clearly saw the spot and compared to their own 6s plus's which you could also see this same mark. I compared my phone to a co-workers and he too had the spot, but it was not as noticeable that my replacement. The Apple store took care of me and get me yet another new one which has the spot, but it was much more faint.

Has anyone else noticed this apparent inherent problem with the 6s plus? To me it seems like there is something internal that is pressing on the screen from the inside.