Your iPhone's Calendar app can subscribe to your Gazelle calendar link, so your appointments show up next to your other calendars. Events update when they change in Gazelle, but you can't edit them on your iPhone. To bring your iPhone events into Gazelle too, see 2-way calendar syncing in Gazelle.
Before you start, turn on sharing and copy your calendar link. See Share Your Gazelle Calendar With Another Calendar App. If you copy it in the Gazelle mobile app on the same iPhone, it's ready to paste.
Add the calendar on your iPhone
Open the Settings app and go to Apps > Calendar.
Tap Calendar Accounts > Add Account.
Tap Other, then tap Add Subscribed Calendar.
In Server, paste your Gazelle calendar link and tap Next.
Leave the user name and password blank, and make sure Use SSL is turned on.
Tap Save.
Note: If these steps look different than your iPhone, check the Apple IOS support page for updates: "Change your Calendar settings on iPhone" guide
To see your events, open the Calendar app on your phone, tap Calendars, and make sure the calendar that starts with gazelleapp.io is checked.
