I want to associate letters of the alphabet with numbers so that when a
letter is put in a cell, a numerical value can be associated. Sort of
like a phone pad-I want it so that you could put the letter in a cell
and a designated number would automatiocaly show up in another cell. ...

One way is to use VLOOKUP.

Get started by putting the settings on Sheet2.
- Put the letters in column A of Sheet2.
- Put the corresponding numbers in column B of Sheet2.

If the letter goes into A1 on Sheet1, put this in B1 of Sheet1:
=VLOOKUP(A1,Sheet2!A:B,2,FALSE)

Depending on your case-(in)sensitivity needs, you might want to use UPPER()
or LOWER().