If you call on someone or call upon someone, you pay them a short visit.
to ask or demand that sb do sth 请求，要求，要（某人做某事）
I feel called upon (= feel that I ought) to warn you that…
我觉得我应该警告你…
call on/upon (someone or something) : to ask (someone or something) to do something : to say that someone or something should do something— followed by to + verb
The opposition has called on/upon the governor to resign. [=the opposition has said that the governor should resign]
反对派要求州长辞职。
You may be called upon to do several jobs.
你可能会被要求做多项工作。
Universities are called upon to produce trained professionals. [=it is the job of universities to produce trained professionals]
高校的任务就是培养训练有素的专业人才。