Laying in bed/couch with the phone over your face and arms outstretched. Eventually your arms get tired or a muscle twitches and you drop the phone on your face.
I read or do a crossword in bed as part of my go to sleep ritual. Sometimes it slips out my hand though usually it just hits my chin or chest. I can easily see how it falls on someone's face though.
https://knowyourmeme.com/memes/text-in-bed-drop-phone-on-fac...