How to restore 2025 calendar on iPhone

Sorry posted in error.

Go to settings>apps>Calendar.

Look at the value for "Sync".

You can set how far back the calendar will keep events synced.

I'm not sure what you mean? On my Calendar app on my iPhone I can see past years calendars by tapping the back button (<) at the top left of the calendar screen. And all calendar entries I've made are still there.