Synchronize Calendars between iPhone and outlook?

Hi Eddytsang,

You should be able to view all your accounts on your Calendar if they are enabled in your Settings. Let's have you check this out to see if they are all set correctly:

Set up iCloud, Google, Exchange, or Yahoo calendar accounts

1. Go to Settings  > Calendar > Accounts > Add Account.

2. Do any of the following:

* Tap a mail service (iCloud, Microsoft Exchange, or Google, for example), then sign in.

* Tap Other, tap Add CalDAV Account or Add Subscribed Calendar, then enter your server and account information.

You can also find more information here: Set up multiple calendars on iPhone

Let us know how that goes.

Cheers!

Thanks for reaching out Eddytsang,

It sounds like you want to sync calendars from different providers with each other.

Microsoft provides this guide to Synchronize Outlook and Apple iPhone or iPod touch calendars.

Yahoo provides these steps to Sync or un-sync Calendar and Contacts on iOS.

As for Gmail, you can follow this guide to Add Google Calendar events to Apple Calendar.

Hope those steps work for you to use these third-party calendars with your Apple calendar.

Take care.