Presumably you are using an email app on your Samsung phone in order to access your email and that no other person has access and could be deleting the emails.
You will need to check to see if it is set up as an IMAP account or as I suspect a POP3 account. You can do that by accessing the email app settings.
If you have set up the email app as a POP3 account it means that the phone's email does not synchronise with the BT servers so if you delete an email on the phone it will not show as deleted on your laptop and vise versa.
If you check the settings and it shows that you have set the phone up as a POP3 account, you need to look through the settings to see if there is an option to "Leave Message on Server" and that the box is checked. There may be a sub section that gives an option to leave on server for a specified number of days.
If there is you need to make sure that the box is not checked and that it does not specify any days.
