How do you stop doomscrolling at night without giving up your phone?

Change what is available rather than relying on stopping once you have started, because the feed is engineered to make stopping hard. Practical steps: remove news and social apps from the home screen or the phone entirely, set the phone to greyscale after a fixed hour, charge it outside the bedroom, and put something else within reach — a book, a notebook. If you use the phone for an alarm, buy a cheap clock. Also useful is naming what you are actually looking for, since doomscrolling is often a search for reassurance that the feed is structurally unable to provide.