When you create a new account on windows phone by going to settings > email + accounts, you can also choose to sync the calendar that is included with the account, along with any related email, contacts, and tasks.
Calendars (and their related appointments and events) that are synced to a phone are stored on the phone, but they can be hidden from view in the Calendar hub via the phone’s calendar filter settings.
This article describes how you can toggle the calendar filters on and off.
To filter calendars that are shown in the Windows Phone Calendar Hub:
Open up the Calendar Hub on the phone
Tap the three dots in the lower right hand corner of the screen > settings
Scroll down the list of calendars that are synced to the phone and tap the box to the left of each calendar to enable or disable the calendar view filter, according to your preferences. You can also select the color your want the appointments to display in the Calendar hub by tapping the box below the calendar name and selecting the color your prefer.
In this screenshot, you can see that the outlook.com “work” calendar is hidden from view, and the microsoft account “My Tasks,” general, and “work” calendars are displayed in the Calendar hub.
Filtered calendars are not removed from the phone – they are still stored on the phone and can be displayed when desired.