I came to the very same conclusion - I need "empty time" to reflect, and prepare myself for my own life. For me, it was not smartphones, it started with books when I was a child, and continued with music players and alcohol later. Everything to keep the unwanted thoughts and feelings at bay. I am an excellent daydreamer as well, at times of stillness, I find something to "work on" in my mind.
What I ended up with is literally a time of day where I "sit with myself" and just think about things. I just sit down for some minutes and try to get my bearings on where I am in life right now. Also, I eliminated a lot of background noise and music - I often do menial things without any other distractions for example. Good opportunities to think about something deep.
For me that's when I take a shower. I think I take showers way too long, but it's just a thing I enjoy and I think through many topics then. Sometimes I am sad that I cannot take notes during the shower, but if I could, maybe I would be back to square one.
Alternatively... just let the thoughts be. I think writing them down, or even the compulsion of writing them down, sounds like a kind of anxiety in itself - "this is Important, I Must Remember it and Do Something with it as soon as I'm out!"
But if it's important enough you'll remember or it'll come back to you next time you shower. Or not. Either way is fine.
Same for me. The thoughts came when I was taking a shower, or trying to fall asleep. For me, these times did not work for thinking at all, and I just ended up hating and avoiding both, to tell you the truth. The specific "sitting down with myself" time actually helped me to de-stress these other two, so now I'm much calmer when taking a shower, or trying to fall asleep.
But you can (take notes in the shower). I do and it helps me offload the burden of forgetting those shower thoughts.
It has also made me realize that these fleeting thoughts are not as smart as I thought they were.
I believe one of the side effects of the loss of “empty” time to reflect is that people tend to rush decisions even when there’s time enough to think it through, as it were more important to take a quick decision rather than a good one.
Meditation is such a superpower. It costs nothing - not even time when you realize through meditation that there is no such thing as time, and emptying your mind is a great way to be in the now - it's "easy" in the sense that you don't really need to know anything, just let go of things. Letting go is tricky because we tend do engage with it in an active way and that's already grabbing on to something. Letting go is the opposite of doing anything.
Learning to just sit still and let the universe (including whatever your mind does) flow around you... It makes a huge difference in mental health. It really cannot be overstated how beneficial for humans it is to just have downtime and do literally nothing but breathing.
But I know it's hard. Our whole culture is predicated upon being busy. But we can just put everything down and be empty for a bit every once in a while and it is so beneficial.
What I ended up with is literally a time of day where I "sit with myself" and just think about things. I just sit down for some minutes and try to get my bearings on where I am in life right now. Also, I eliminated a lot of background noise and music - I often do menial things without any other distractions for example. Good opportunities to think about something deep.