Try adding a new event on your phone then check your calendar on icloud.com from a computer to see if the event appears there. If not, go to Settings>Mail,Contacts,Calendars>Default Calendar. Here, make sure you have selected an iCloud calendar as your defult (and not something else like On My iPhone, Gmail, Yahoo, an exchange account calendar, etc.) After setting your iCloud calendar as your default, try adding an event again to see if it appears on icloud.com now.
If your default account setting is correct and it still doesn't sync to icloud.com, add any missing events from your phone's calendar to icloud.com. After the calendar on icloud.com is up to date, on your phone go to Settings>iCloud, turn Calendars to Off, choose Delete from My iPhone when prompted, then after a minute or so turn Calendars back to On. Then try adding a new event on your phone again and see if it appears on your calendar on icloud.com now.
Once you phone is syncing properly, go through these same steps on your iPad.