"We are there."
"Є" is "am/is/are". In this case, I would say, using it would be colloquial, it is omitted in standard Ukrainian.
There are cases, though, where you might want to emphasize the "being" (although, again, it is not compulsory and can be dropped):
— You guys are not in the photo! = Вас немає на фотографії!
— No, we ARE there! = Ні, ми є там! ("є" is stressed)
(In this example, "є" is used to stress that someone/something is there as opposed to not being there - "немає").
— Who is present here today?
— I am present! = Я є!