。
She stood up to answer the phone.
Literal
She [topic-は] phone [to-に] answer [in order to-ために] stood-up.
~ために (in order to) marks purpose, and 立ち上がる ('to stand up') is a compound verb combining 立つ (stand) and 上がる (rise). 電話に出る ('to answer the phone,' literally 'to come out to the phone') is the standard expression — distinct from 電話をかける (to make a call) and 電話を切る (to hang up).