It's a phone call. Taiwan is a nation. China needs to get over it.
That's the thing. Taiwan's not a nation.
It's not recognized by most countries because the Republic of China has a competing (and clearly wrong) claim to the whole of China, and the People's Republic of China has a competing (and arguably wrong) claim to the island/province if Taiwan.
Taiwanese sovereignty is it's own completely fraught matter. It's very likely China wouldn't allow it to happen -- they've threatened military action against RoC if it ever does, and many people in Taiwan don't even want it to happen.
Taiwanese re-integration with China is also extremely unlikely because most people in Taiwan don't want that either. Also the Hong Kong / Macao thing didn't go so well.
So the uncomfortable status quo has held for a long time.
The Taiwan situation has been especially messy because Chinese leaders don't want to lose face, but everyone benefits from trade with both RoC and PRoC. There are even deep economic and trade ties between RoC and PRoC despite the standoff.
The US solution decades ago was to cut off all official diplomatic relations, but to leave
a backdoor to relations. This has worked and been a stable solution until the RoC and PRoC can decide on the fate of their political status and the whole "
one China" thing that is the official stance of
both the PRoC and RoC.
Like this is very serious because it's one of the most likely hotspots for a war in east asia that nobody wants.