I understand by the context that it is referring to a gift（礼物）for 李芳. And the sentence is translated like "this one is for 李芳."
But why is 要 in the sentence? Cause if it has the function of a modal verb then it must be put before 是 which is the verb, and also it can't be a verb cause 是 already is the verb.
Why not just something like "这一个是给李芳的。" ??