Open the message in Senly and click the spam icon in the action bar. Senly moves the message to the Spam folder and reports the signal back to the provider (Gmail/Outlook learn what should be treated as spam).
Is it phishing impersonating a recognizable brand (e.g. fake DHL, fake bank)? Forward the message to the real organization (e.g. `abuse@dhl.com`) as well — that way they help take the phishing campaign offline faster.