Hi,
today I had the same issue with an iPhone 4S!
In my situation it was caused due to a bad quality of the replacement digitizer (incl. LCD). When I looked at the borders of the Digitizer, the left side of the black frame border was a little bit higher than the other side.
Due to this quality fault the LCD gets pressure from bottom and it causes white ghost effects on the outlines.
Will return it and order another one from another shop.
Good luck!
Best regards,
Tolga