Some devices can natively sync device calendar to your Google account (both ways), and some, - it looks like only one way (from the Google calendar to the device, but not the other way around).
I have a Motorola phone that works as the former, but my Samsung tablet works as the latter. I forgot all the details, but somehow Samsung calendar cannot sync directly, only via an additional app.
When you create a new event on your phone, does it show up on the Google Calendar server? I.e. if you look at your Google calendar via web-interface, - do you see it?
If you do, - it means you can sync it both ways. And then, you should be able to sync events created by Aquamail to your Google calendar server. Then, you need to figure out in which calendar does Aquamail create its events. What might be happening is that Aquamail saves these events to the "built-in" calendar that doesn't get synced to the Google Calendar.
You can see that on your phone: if you open the even, check which calendar that event is in (often, you can move it to a different calendar right there). If that's the case, - you'd need to figure out how to force Aquamail to sync to the correct (Google) calendar.
I don't have first-hand experience with that, as I am not using Exchange. There was some recent discussion, - so try searching these forums for that.
Alternatively, and especially if you device's calendar cannot be synced "up", you can use a separate app that would do that syncing for you.
