How do I remove subscriptions when these options are not available on my phone?

Use these instructions:

1. Open the Settings app.
2. Tap Calendar > Accounts. Or if you use iOS 13, tap Passwords & Accounts > Accounts instead.
3. Tap Subscribed Calendars.
4. Look for a calendar that you don't recognize. Tap it, then tap Delete Account.

Extracted from the support article that led you here.

Regards

Giulio

It's possible that you may have received a spam calendar invitation on your iPhone that you want to remove. Here's how to do it:

1. On your iPhone, go to the Calendar app.
2. Tap the "Calendars" button at the bottom of the screen to view a list of your calendars.
3. Find the calendar that you want to delete and tap on it.
4. Tap the "Edit" button in the top-right corner of the screen.
5. Scroll down and tap the "Delete Calendar" button.
6. Confirm that you want to delete the calendar by tapping "Delete Calendar" again.

If you believe that you may have received a virus through the calendar, it's important to also check for other signs of malware on your device and take steps to protect your device from future threats. You may want to consider running a malware scan on your device and installing antivirus software to help protect against viruses and other malicious software.

If you continue to experience issues with your device, it may be helpful to contact Apple Support or seek the assistance of a trusted technical support professional.

R4FTY,

An iPhone, unless jailbroken, cannot get any viruses or malware.

The issue shown in the Author's screenshot is typically a spam/scam attempt. That rogue calendar account must be deleted.

Regards

Giulio