I figured out what the problem was for me -- it was embarassingly stupid so you may have already thought of this, but just in case.  On my iPhone the default for calendar entries seems to be my "Home" calendar, which is in iCloud.  But in order to have it appear on my google calendar, I need to change it to the "exchange" calendar - which is linked to my gmail. You do this by scrolling down to the bottom of the entry and selecting Calendar.  I have not figured out how to make the exchange calendar the default -- or maybe I need to set up my iCloud.