I figured out what does it mean. Your phone also records your sleep time, but it only detects the moment you stop using your phone and the moment you pick it back up so there is no detailed sleep analysis obviously. And it is just the chart you posted, shows full hours. Your watch also records your sleep time and naturally it is more detailed and accurate. But when there is two records that overlaps the detailes are not shown in Shealth. So all you have to do is delete the record that your phone held(you can delete it by clicking the edit button at the right top of the sceen) When only your watch record is left you can click learn more and see the full deteails of your sleep analysis.
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