Recovering deleted digits from saved contact on iPhone

I received a text from somebody "This is Joe's number." When I saved it as a contact with his full name etc. I accidentally deleted the last 2 digits of the phone number.

How can I find out the number? My phone received a text message from the number, it seems like there should be a way to find out what it was. But now the contact name displays at the top of the message, rather than the number, and if I click on the contact at the top, it displays the number I saved rather than the number the message was actually sent from.

Help?

[Re-Titled by Moderator]