The email folders on my iphone and pc are not aligned, presumably because one is setup for POP and the other is IMAP. My pc email is Outlook and there's no option within Settings to view the email server setup. Is it possible to change whichever is POP to IMAP and if so, will I lose all my history?
use thunderbird instead and import all email accounts into there
assuming you using this on a pc
currently have gmail ,outlook and BT email account all working fine in here

First of all, whichever client you use it is not possible to change from POP3 to IMAP on the fly, the account has to be deleted and recreated.
Any client configured as POP3 downloads the mail to the client and unless the box to retain a copy on the server has been ticked, the mails are deleted from the server.
Any sent mails or mail folders created on the client do not appear on the server.
You can check the server settings in Outlook. see the following links for the way to check and for the correct settings
https://help.one.com/hc/en-us/articles/360000338198-Where-can-I-find-the-server-settings-in-Outlook
You can not change POP3 account to an IMAP account on the fly. You would need to delete your POP3 account and then set up the IMAP account.
Before doing that you would need to check all your emails are still on the BT servers, which they should be as they are showing in your IMAP account, so that they can be downloaded.
POP3 does not store sent emails or folders on the BT servers, they are stored on the device, so you would not be able to download them and if you deleted the account you would lose them unless you back them up.
On which ever device has the POP3 account you could try leaving the POP3 account as is and also set up your BTMail account as an IMAP account using a different email app
It would show your BTMail account as it is on the BT servers and you could try dragging and dropping or copy and paste your POP3 emails/folder into the new IMAP account.
I have never done that so I do not know if it will work so you try it at your own risk.