Looking on the internet deeply has found these results:

i am in a meeting is the most popular phrase on the web.

i am on a meeting 1418,000 results on the web	i am in a meeting 1969,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Our president wants a meeting next week. Saw you scheduled a meeting with Mike. Mentioned something to McCall about a meeting tonight. A meeting with a financial advisor is practical. We have a meeting to attend downstairs. Prince Condé requests a meeting with the king. Pending a meeting with the director. The CRO wants a meeting tomorrow.	The CRO wants a meeting tomorrow. Saw you scheduled a meeting with Mike. Prince Condé requests a meeting with the king. We have a meeting to attend downstairs. Our president wants a meeting next week. This had better be important, 'cause as you can plainly see, I am in the middle of a meeting. I am in a meeting with Dwight, Robert Dunder, and his niece. I am hosting a meeting in the near future, to which it seems some parties would like to be privy.

i am on a meeting

1418,000 results on the web

i am in a meeting

1969,000 results on the web

More popular!

The CRO wants a meeting tomorrow.
Saw you scheduled a meeting with Mike.
Prince Condé requests a meeting with the king.
We have a meeting to attend downstairs.
Our president wants a meeting next week.
This had better be important, 'cause as you can plainly see, I am in the middle of a meeting.
I am in a meeting with Dwight, Robert Dunder, and his niece.
I am hosting a meeting in the near future, to which it seems some parties would like to be privy.