있다 / 계시다
January 28, 2016
June 25, 2018
Updated: July 22, 2018
Sorry for the late reply.
계시다 is said to be the honorific form of 있다, and this is half true.
This is because 있다 has two main meanings - (1) to be/stay at a place; and (2) to have (something). 계시다, on the other hand, only has one meaning - to be/stay at a place.
In sense (1), 계시다 is pretty much used exclusively as the honorific and the usage of 있으시다, while it would be understood, is not considered standard. Example: 집에 계세요? is "are you at home?" (honorific). 집에 있으세요? would be far less common (and considered less correct).
On the other hand, 계시다 does not mean "to have" (honorific). In this sense, you would use 있으세요? Example: 돈 있으세요? can be taken to mean "do you have money?" (honorific). The use of 계세요 here would not be correct.
Hope this answers your question.