LEDs degrade in brightness over time, this is well-known information. It is no different for OLEDs. In standard LED backlit displays, the LEDs all share the same power-on hours and brightness, so they don't affect the image uniformity when they degrade since they all degrade together. The only effect is that the display will have a very subtle loss in brightness over time that will almost never be noticed by anyone.
Since OLEDs are used as individual pixels, the pixels will not degrade in a uniform manner, it will depend on the usage of every pixel. The damage is also very different from plasmas, so the same solutions do not apply. Unlike plasmas, where the pixels can develop a discolored spot due to the heat if left active too long (hence the name burn in), OLED degradation has nothing to do with how many hours in a row it shows the same image. Moving the image around doesn't "reset" the burn-in counter (because OLEDs don't really "burn in", they degrade slowly over time). Every hour you use an OLED for is another hour of wear, it doesn't matter whether you break the time up into smaller chunks or have it all at once. So the common advice of "just avoid static images" is misguided here. Although the symptoms look similar to plasma burn-in, the nature of the problem is entirely different from plasma displays, so the same solutions do not apply here.
Of course, having the same image on the screen will cause that particular image to be worn into the screen more than others, so avoiding long static images is recommended, but only because avoiding cumulative hours of the same image in general is recommended for avoiding OLED degradation. It doesn't matter whether the hours are all in a row or not. Screensavers won't protect OLED screens or undo the degradation, they'll just degrade the screen more with a different pattern. The only screen saver an OLED should have is a black screen.
OLEDs don't like being exposed to oxygen, but AFAIK that's just a manufacturing challenge for the plant to deal with, properly designing the screen to be sealed from outside contaminants, not something that affects panels over time.
Worth noting I've also been using an OLED phone for the past year and a half, no regrets. But then again I did turn off the software navigation buttons