Is there a way to transfer bookmarks from iPhone Map app to Google Maps online? I understand why I can't, but has anyone found a workaround?
There is no way to synchronize Maps with Maps (so to speak), but you can sync Earth with Maps, with Google Earth being on the iPhone. If you log in to Google Earth, it will synchronize your maps. Those can be added from Google Maps on the web. Unfortunately, there's still no way to add stuff from an iPhone, but there isn't no connectivity between them.
Because I think that was a really messy and hard-to-understand answer, here's a clearer synopsis:
I'm sorry there's no way to do what you want in a native Google app!