idk how to compare those sentences と I bought this phone at 2001. and I bought this phone in 2001.” I thought it was same tho TvT” はどう違いますか？説明が難しい場合は、例文を教えて下さい。

The first sentence makes sense if you purchased the phone at a store named 2001.

The second sentence makes sense if you purchase the phone in the year 2001.

You do not use the preposition "at" when referring to years.

You can use it when referring to time, such as "I bought this phone at 4 P.M."