Explain me please the exact meaning of the verb 계시다
Somebody, help me please! Is 계시다 the polite form of the verb 있다 only? Or 이다 also can be replaced with 계시다?

Question

Answer

Hello

계시다 is the honorific form of 있다
In this case 이다 cannot replace 꼐시다

If you want use 이다 in a honorific way, you can use the honorific maker 시
~이십니다 (Very formal)

Or a slight less formal way
~입니다 (Formal)

Another verb example is 
먹다 = to eat.
The honorific form is 잡수시다

Thank you :)

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