Find someone with a phone number?

Call… the phone number?

White Pages reverse phone lookup. Or just try Googling the name and/or phone number.

try 411.ca Reverse lookup

@toomuchcoffee911 Agreed.

Is that all that you know about the person?

http://www.yellowpages.com/findaperson

http://www.whitepages.com/reverse-lookup
http://www.intelius.com/search-name.php?searchform=name&
Either of these works very well.

Use a reverse lookup.

Yes, there are a lot of sites, that allow you to find someone by their phone number or vice versa. Most of them are paid. Search Google to find the most acceptable for you.
I just can recommend this one: reverse phone lookup

Good luck