1.
If you call someone in , you ask them to come and help you or do something for you.
Call in an architect or surveyor to oversee the work.
PHRASAL VERB : V P n (not pron)
2.
If you call in somewhere, you make a short visit there.
He just calls in occasionally...
I got into the habit of calling in on Gloria on my way home.
= drop in
PHRASAL VERB : V P , V P on n