Like a lot of these tips, it’s going to depend on which phone you’re using.
Currently, I’m using the OnePlus 6T phone and it has a setting called “reading mode” that is in greyscale. It’s an option found under the display settings.
More and more Android phones have some variation of “night mode” that you can schedule for certain times of the day. Most of those night modes have a monochrome or greyscale option.
If your phone doesn’t have a “night mode”, you can also find some additional display options under “System-Accessibility-Display”. There are some color correction options designed for users with colorblindness and other vision impairments, but it’s also a great tool for those of us who want to look at our phones less.
Hope that helps. Thanks for reading!