Hi Kuddel,

Thanks for posting here.
I understand you have set up Exchange ActiveSync on your mobile device (Android device) and currently, the issue you are experiencing is that calendars can’t  by synced from Outlook client to mobile device even though, it can be synced from mobile device to Outlook successfully.

Based on this situation, to troubleshoot this issue, would you please refer to the step-by-step article to reconfigure Exchange Online account on your device to see if any improvement?

Set Up Exchange E-Mail on an Android Mobile Phone
http://help.outlook.com/en-us/140/dd940179.aspx

If this does not help, you may also try to update the server settings on your device to the host name address.

a. Go back to the main page of Outlook Web App. In the top right corner, click on the question mark next to Options and then select About.
b. On the About page, you'll see the entry for the Host name listed.

c. Use the value next to the Host name as the server setting on your mobile device.

Thanks,
Grace Shi