Two iPhones on one apple account

I purchased an IPhone for my wife a couple of years ago. Now I have purchased a new phone for her so both are now registered to my original account, and both phones synchronise with messages, photos, contacts.

I want to delete the account from the first phone so I can use it separately but am concerned that she will lose all contacts , photos etc if I cancel the account on the original phone.

i imagine I should be able to detach the first phone and set up another account without affecting her account.

any advice appreciated

thanks