You need to connect to the same calendar provider on both you phone and eM Client.
Who is you email provider Christian?
So I had a look and they do provide an online calendar for your account. If it was not setup automatically in eM Client when you added the email account, you can add it as a CalDAV account. Go to Menu > Tools > Accounts and add a new account. Select Calendar > CalDAV.
The default calendar app on the Samsung phone is also able to connect to CalDAV calendars. Follow their instructions on how to do that.
Once that is done, you will have a synced calendar on both devices.