Diplomacy is a complex and delicate game. At its core, it is desgned to prevent major powers from going to war - which with nuclear powers could kill billions and end civilization. So it provides lots of ways that countries can signal their intentions long before there is any risk of war.
In some ways its like the federal reserve: The chairman of the fed doesn't come out and say "I think the economy is screwed for the next few years", that would cause wild market fluctuations. He gives small hints as to the gradually changing probabilities of interest rate changes - and the markets can respond in a gradual way.
The US, China and Taiwan are currently in a situation where no one is killing anyone. Where there is hundreds of billions of dollars of trade. This is to be contrasted with the situation in the 60s where a cross-straight war was a real possibility - a war which would at best have killed a huge number of people can cost the US a vast amount of money, and at worst...
There are issues. China is building bases in the south china sea. China is stealing technology. The US is delivering high-tech products with NSA spyware. Japan is trying to revive some old WW2 island disputes. Some factions in Taiwan are trying to create problems with China to snub other factions.
But despite those issues, we are able to buy low cost Iphones and TVs, cargo ships move through the area unmolested, China and Taiwan are both getting rich off of mutual trade. Boeing is selling vast numbers of airliners to the rapidly growing Chinese airlines. American companies are designing huge buildings in China. In general things are not that bad.
I see no reason to throw out the one-China policy when all we need is to continue our various diplomatic tweaks. They are working.
Tell me you're not serious. Are you really concerned about his accepting a congratulatory phone call from Tsai? If so, you're unfamiliar with the US - China relationship.