The iframe fills the screen, and overflows just a little bit. I tried modifying the inline CSS of the iframe tag to:
<iframe src="https://outlook.office365.com/owa/calendar/DKPuhutaanpilvest@digikuu.fi/bookings/" height="100px" width="90%" scrolling="yes"></iframe>
After adding the new iframe directly to the editor without containers or paddings, and I reload the page on my phone, the inline CSS seems to work for a fraction of a second, and then turns full width again and overflows the screen.
Note: This only happens on my phone, I haven’t been able to replicate the bug elsewhere. On my friend’s phones the website works fine. I’ve tried refreshing all my browsers caches, tried with multiple browsers, refreshed servers cache, but still nothing.
EDIT: If you check out the link, you can now see that there are two iframes. One in the original spot, and one plainly added through the editor without any containers.