Wired suggested using grayscale mode to help make the phone less engaging. On iOS, I believe you can find it under Accessibility > Display & Text Size > Color Filters.
https://www.wired.com/story/grayscale-ios-android-smartphone...
https://www.wired.com/story/grayscale-ios-android-smartphone...
For eye strain, use the Reduce White Point setting combined with minimum brightness at night.