Apple watch and family share

I just noticed that There is family share for AW but looks like it is only meant for family members without iphone. My situation is that i have kid who has iphone and AW SE. AW is used when he is in school or out with friends and therefore he is only carrying iphone at home or when he goes to sleepovers/special cases. So he is using same number for AW and iphone. Is There a way to setup AW for family member with iphone. I would like to benefit school time option just like can control iphone screentime from my own iphone