Top search should be able to search for

Top search should be able to search for direct phone numbers and extensions

I would like to enter user's direct phone number or extension in the top search bar in the app in order to allow to identify a user.

Customers have/use 2-5 digit extensions
Searching with the "contains" method would be best, as e.g. for the "starts with" method it is uncertain forthe customer, if the local area code or even the country code have to be added or not. Customer expectation is "contains".
Search by number in the external contacts (phone lists) is also a common use case and requested. Customers are in the calling section of the app and have a search field with the text stating "search" - of course they are expecting to search for a number.