I've never tried the apps that claim to track your sleep, so I will not comment on those. But recently I was about to buy a consumer fitness band until I read a couple of technical reviews that show how they are all essentially worthless except for the Apple watch. Here is reviewed an iOS app but since the Apple watch is not mentioned, I don't know how precise his measurings are. IMHO the phone alone is not enough to track your sleep cycles meaningfully.

Anecdotally I've noticed that when I smoke weed I don't remember what I dreamt, every single time. I suspect it alters my sleep cycle in some way.