This is something that @Cam Adair and @SlackRamen have talked to me about before, but I have finally activated greyscale on my phone as part of my efforts to focus. The theory is it is less appealling so you don't want to look at it as often.

 

If anyone else is on Android and wondering how to do it, the link is here. Not sure how to do it on iOS but I am sure someone has a link for that too.

 

I've also got a flip cover for my phone to not only protect it a bit better (to stop spending money on replacing screens) and because I remember them being annoying to use.

For iPhone...

Settings:

General

Accessibility

Display Accommodations

 

Color Filters:

Tick Grayscale.

Optionally, from Accessibility, click Increase Contrast

and Darken Colors.

 

Note that for some reason, screen snaps still come out in color.