Apple Watch series 6 not tracing stairs

Iphone 12 with iOS 15 and apple watch series 6 (Nike version) also updated to 8.1 but if I am not holding my phone with going up a flight of stairs, the watch will not record it as part of my activity. Both devices have to reset and resynched and the issue is still there. When I open the fitness app on my phone, steps and flights climbed does not show the true number of flights climbed unless I hold the phone. I thought having the watch negated needing the phone while exercising