If there are some apples in a basket that are sweet, then this is natural..
- The apples in that basket are sweet
Sorry if my earlier reply was confusing. The phrase also means that apples that are freshly picked - in the picker's basket - will taste sweeter than ones bought in a supermarket. (But I guess you didn't mean that..)
If I was walking past a market-trader and he said "The apples are sweet in the basket!" then I would know exactly what he meant and I might buy some. I would understand him, in part, because of the phrases mentioned above
If I were an ESL teacher (which I am not) I might say: "in the basket" is an adjectival phrase and, in th