where is the verb???

I'm in the urgent meeting now.

It does not need any verb in this kind of sentance structure. It describe a situation instead of an action.

Other examples:

I'm in the bathroom vs I'm using the bathroom
I'm on a bus vs. I'm riding on a bus


Unless you want to say I'm leading / attending an urgent meeting now. By the way, it is better to use an urgent meeting instead of the urgent meeting unless the reader knows which you are talking about. So basically there is no grammatical error.

No grammatical error,
"am" is the verb.

I am in the urgent meeting now. ←The verb is am meeting

is there any grammatical error? ←The verb is is

there isn't any grammatical mistake in here.
"am" is the verb.