I recently noticed that calendar entries I entered into my iPhone were not syncing to my Hotmail calendar and, therefore, not being shared with family members who shared my Hotmail calendar. I have a Windows 8 laptop and an iPhone 5.
I'm not sure when the entries stopped syncing to and from Hotmail from my iPhone. After various attempts to remedy the problem, my only solution was to delete my Hotmail calendar from my iPhone and re-add it as an Exchange account rather than an Outlook account.
Before removing the Hotmail calendar from my phone, I compared my iPhone version of the Hotmail calendar and my laptop version of the Hotmail calendar and added the entries from my iPhone which did not previously sync to the laptop version of the calendar.
Here are the steps:
1. Compare iPhone version of your Hotmail calendar with your PC version of the calendar.
2. Add any entries to the PC version which are present on your iPhone, but not on your PC version.
3. Delete your Hotmail calendar from your iPhone by using Settings (Mail, Contacts, Calendars) on your iPhone.
4. Re-add your Hotmail calendar, but choose "Exchange" rather than "Outlook.com" to enter the account.