If lowering brightness doesn't make you feel better with this, I'm afraid nothing else will do. After all, this is an LCD display, it needs backlight. This is the main difference between OLED and LCD. OLED pixels emit light by themselves, LCD ones need light from the back to be visible.
That's the way the phone works, I don't think you can do anything about it but lowering the brightness and making the backlight a little less intensive. And this is a tradeoff for having real, natural colors - OLEDs are very oversaturaded in general, and they can't be used with XReality/Bravia engines.
