Small white dot on my iPhone screen

Once you know it's the screen, check the warranty before you pay for anything. If there's no crack or dent and it's still covered, Apple will sometimes swap it under warranty, pressure marks are a grey area so it depends on who looks at it. Quick check on what you're dealing with: open a pure black image full screen. A stuck pixel stays a sharp bright point. A pressure mark mostly disappears on black and shows on white.

Take a screenshot first. If the dot shows up in the screenshot it's software (an AssistiveTouch button or some accessibility overlay). If it doesn't, it's the panel itself. A soft white blob that's most visible on grey or white backgrounds is usually a pressure mark on the backlight layer, often from something pressing on the screen in a pocket or bag. That doesn't fix itself, the only real fix is a screen replacement.