The islands weren't being militarized until after the call to Taiwan, now the Chinese are putting weapons systems onto those islands; it's a very clear diplomatic signal that they're pissed.  Also, you seem to be unaware that the Chinese already have advanced weaponry including nuclear weapons,

The call to which you refer was arranged weeks in advance by Taiwan, they pushed the right buttons and paid the right K street lobbyists who convinced (read manipulated) Trump into taking the call.  All they had to do was play to Trump's ego telling him he's the president elect and he can do whatever he wants now.  The call was a major coup for Taiwan and they got exactly what they wanted. I love it when people try and play it off as if it were some spur of the moment call to say congrats, I can't believe people actually fall for that line.