I have shared my Outlook.com calendar with my spouse, also having an Outlook.com email id, as co-owner. She is able to view & modify the calendar events using the outlook.com web app, but they do not sync to her cellphone (Nokia Asha 310)

Nokia Asha tech support replied stating that only one calendar - the one set as default in outlook.com - is supported in the Mail For Exchange app. Therefore, I was instructed to set the shared calendar as default in my spouse's outlook.com account. But, the shared calendar is not listed in her outlook.com "Primary calendar" dropdown list. The list only displays the calendars that she has created herself.

Appreciate your assistance,

Hemant