Pheno hunting is not always breeding related. It’s essentially so you can find the most desirable plants out of say, 10 females. The purpose is to identify which plants grown from seed perform the best according to your criteria- yield, flowering time, terpenes (taste and aroma), structure, stability, or difficulty of grow.
You could do this for your home grow to find your ideal ‘favorite’ plant to clone and grow out repeatedly, or you could do this for a commercial grow to find the best plant to crop out perpetually.
You can use this for breeding to find the best candidates to breed, as you said, selective breeding.
The reason i would pollinate 9 females with 1 male is because it makes sense to pollinate 9 females once instead of pollinating 1 female times 9 runs. So I could make 9 crosses at the same time, doesnt mean i would focus on them all equally.