Unless you set a default iPhone calendar, the iPhone chooses to place all of your new calendar entries into the iCloud calendar if you are connected to iCloud. This is the calendar that the iPhone picks when you press the plus button or use Siri to add an event to your calendar.
It is important to make sure you set the default iPhone calendar to one that you can access on all of your devices, including a tablet and your computer.
Until you set the default iPhone calendar you may only see appointments on your iPhone or iPad and you may not get the reminders that you need across all of your devices. This is especially important if you use Gmail for your calendar or a work calendar on Outlook or Exchange.
If you are reading this you either just set the iPhone up for Gmail or a work email, missed an important meeting or you are just sick of changing the calendar information on your iPhone every time you add a new event.
How to Set the Default iPhone Calendar
You can set the iPhone default calendar from the settings in under a minute. You will need to already have the calendar information connected to your iPhone. This works with all calendars on your iPhone including work calendars, Gmail or Google calendars and all of the shared calendars that these have connected with the iPhone.
Find the Settings icon on your iPhone home screen and tap on it. This process is the same on the iPhone, iPad and iPod touch. You will need to perform this on each device individually as these options do not sync from one phone to the next.
In the Settings app find Mail, Contacts, Calendars. Tap on this to open additional settings.
Scroll down to the Calendars section.
Tap on Default Calendar -> Choose the calendar that you want to set as the default iPhone calendar.
After you choose this you will be back on the Mail, Contacts, Calendars setting and you will see the new default iPhone calendar.
You can do this with any calendar that you want to use. If you need to enter a lot of calendar entries to one calendar, you can set that as the default and then set it back. On this screen you can also change the time zone settings, week numbers, add alternate calendars and default calendar alert times so you always have time to get where you want.