Settings → Apps → Calendar → Accounts →
Add Account → Other → Add Subscribed Calendar, then paste the link.
Google Calendar
On a computer: Other calendars → + →
From URL, then paste the link. It then syncs to the phone app.
Outlook
Add calendar → Subscribe from web, paste the
link, give it a name.
Updates arrive on your phone's schedule, not ours. Most calendar apps
check for changes every few hours, and some are slower. If a change is
urgent, expect a phone call rather than assuming the calendar reached you
first.