質問: I'm a bit confused by the usage of さしあげる in this sentence from Kanji in Context: ただ今、来客中ですので、後ほどこちらからお電話さしあげます。 We have a guest at the moment, so we'll call you later. To me, お電話いたします or even お電話いたしてさしあげます are more grammatical. Maybe it's really お電話(を)さしあげます? (I'll give you a call).
回答: [差]{さ}し[上]{あ}げる is [謙譲語]{けんじょうご} for words like あげる and やる, as well as してあげる. By itself it means *to give* (with a sense of great respect), and as a subsidiary verb ([補]{ほ}[助]{じょ}[動]{どう}[詞]{し}), it adds a great sense of respect (for the person receiving the action) to the verb it is helping. [致]{いた}す is basically 謙譲語 for する. `電話(を)する(いたす)` can be thought of as: "to call". `電話(を)してあげる(さしあげる)` can be thought of as: "to give a call". In the sentence, the callee is telling the caller to expect a call back. This creates a sense of "waiting"; so, instead of just "calling", the person will "*give* a call back" (i.e., 電話をしてあげる). However, in business situations 謙譲語 is preferred on the phone. So, the frank-sounding `してあげる` becomes `差し上げる`. As to `お電話(を)いたしてさしあげます`, converting back from 謙譲語 would yield `電話(を)してしてあげる`, which is blatantly incorrect.