The best suggestion I have is to download a "screen test" app that runs the screen through showing solid panels of all of the colors. If that spot remains through all the tests, it's a stuck pixel. If it's a real nuisance and the phone is relatively new, it might be a warranty item.
I run all my phones through a screen test as soon as possible. It's a lot easier to exchange one with dead pixels on day one. Never actually encountered one - LCD/AMOLED panel build quality has improved a lot in the past few years.