The term "phishing" relates to email scams where unsolicited messages are sent by illegitimate senders, usually posing as a recognised brand or organisation.
These emails may attempt to trick you into disclosing personal or financial information. Sometimes the email may contain a virus hidden within an attachment, which if opened, could be harmful to your computer.
Please see the link below for BTs process on reporting Phishing: https://www.bt.com/help/security/how-to-report-abuse-and-phishing.