The issue is whether to a reasonable outsider, like the Yellow Pages, it would appear that you had authority. Other people are entitled to rely on what reasonably appears to be your authority, and if, based on your title, position, what you told the Yellow Pages, etc., you would seem to have the authority to execute a contract like this, they can hold your employer to it. Consider if this were not the case, any business could get out of any contract by saying after the fact that the signor lacked authority--that's why outsiders may rely on the appearance of authority, to prevent that sort of manipulation. If you truly did not have authority, then your employer may be able to sue you personally for the money you improperly obligated them to pay.