There are a number of ways you can do this: you could create a
userform, for instance. Since you're starting from scratch you have
the ability to customize the data in / data out process, and you will
look like a genius if you set it up to be most convenient for the end
user. Do they need to print this info? Do they need to enter 10 at a
time? If you can determine the issuing company by the first 6
characters, are you going to require the users to enter all 15 digits?
(People in a production environment hate that kind of thing.)

The easiest way to do this, to my tiny mind, would be to have a
workbook with two tabs: one that allows user input and returns results,
and one that stores the credit card company info and phone number (this
tab could be hidden, if you like). Set up a column of 10 or so cells
for the user to enter those 6 digits; right next to it set up a VLOOKUP
formula that matches the 6 digits to the issuing company data and phone
number.

If you'll post some different examples of data (specifically, the
number of characters that may be used to match) and the desired
outcome, someone here on the newsgroup can help you with the exact
formulas.

Good luck with it!