に電話を掛けて

call on the phone

→ に
phrase Rare #42,206
call on the phone Used when calling someone by telephone; the final て form can connect the phrase to what follows, meaning “and call” or “after calling.”
JA: 仕事が終わったら、母に電話を掛けて。
EN: Call my mother when you finish work.

彼女は昨夜大変遅くに電話を掛けてきた

She called me very late last night.

私は彼に電話を掛けて予定を尋ねた

I called him and asked about his plans.