How to clear virus from my phone

Oh, that nuisance.

Do note that it is not a virus, not a hack. The bogus calendar entries appeared as a result of you accepting an offer from a web site to “Send Notifications”.

If running iOS 13 or earlier versions, check: Settings - Passwords & Accounts - Accounts - Any rogue entries here? If so, delete the rogue account. 

If running iOS 14, check: Settings - Calendar - Accounts - Any rogue entries here? If so, delete the rogue account. 

Please describe the symptoms you are seeing that lead you to believe there is a virus.

You are quite welcome.