Matrix allows you to search for agents by their phone number.
Go to Search> Agent Search. The Agent Phone field is in the top right of the search screen.
When entering the phone number, it has to be done in a very specific manner, or else you will not find any matches.
It has to be in the following format (as displayed in the screen shot above)
There has to be parentheses surrounding the area code, then a space, then the phone number (with a hyphen in the middle).