yes, that's right

I answer.

私は答えます

I answer briefly.

私は短く答えます

I answer briefly that it is right.

私は「そう」と短く答えます

I answer briefly on the phone that it is right.

私は電話で「そう」と短く答えます

I answer my friend briefly on the phone that it is right.

私は友達に電話で「そう」と短く答えます