Possible to use Sleep with only my Garmin (Fenix 6X Pro) with phone off/different room?

I use the above combination and I am happy about pretty much every aspect of how it works. As I understand, the watch is what is recording all the relevant data (though I’m not sure about sounds ?), so I have been thinking about turning my phone off or putting it in a different (distant) room at night as so many specialists advise for better sleep. I am wondering if that is a viable thing, and which one would be the preferred option ? Does the watch record and store all it needs until it gets to sync with the phone again in the morning ?

I know about airplane mode, but I would prefer to get rid of the phone altogether at night, since I have many things and notifications that pop up even without internet connectivity that I find myself eagerly checking for in the mornings.