asking for password when backing up onto new phone? trying ti get contents onto new phone

Do you mean backing up the phone, or restoring a backup onto the phone ? If restoring, what is the text of the message/prompt that you are getting ? If the backup is encrypted you will have to enter the encryption password to restore : About encrypted backups in iTunes - Apple Support

Is the backup and it's asking for the encryption password ? If so you won't be able to use the backup if you can't remember it