in a query by example grid, where it shows the new field (you will need a new field for the merged data) change the text to
PhoneCode & " "Phonenumber
(obviously change these to whatever your fields are called)
dont know how you would incorporate it into your form as i cant see your form. then you could run a report and grab the full numbers from there (copy and paste) [i hope].
if you get stuck, send me an e-mail so i can send back an attachment.