Are you already lying in bed before you start scrolling, or do you pick up your phone right after you've settled down to sleep?
The thing is, the screen shines directly into your eyes, and your brain gets the signal "it's daytime now, stay awake" - melatonin production drops. Plus scrolling is this endless stream of new stuff, and every next post could be even more interesting, so your brain doesn't want to let go of the phone. It's like with chips, but for your attention.
The easiest thing is just not to take your phone to bed at all - leave it in another room or at least on the dresser. I know it sounds radical, but I tried it and fell asleep way easier. If you absolutely can't give it up, at least turn on reading mode or a yellow light filter and try not to scroll through feeds - read something calming instead, like articles or a book.