I think this is perfectly acceptable.
Firstly, on the basic premise of independent democratic national sovereignty:
(a) the US president-elect is within his rights to chat on the phone with a democratically elected president of an independent sovereign nation.
(b) the US president-elect is the elected president of the US people, and his role is to represent the United States, not the foreign policy objectives of other nations such as the PRC.
Secondly, on the foreign policy position:
(a) the whole "One China" principle and the notion of the US kowtowing to PRC internal political discourse for over three decades is confused and contrary to a number of political principles (sovereignty, democracy, human rights, self-affirmation) and the US demeans itself by complying, notwithstanding that it is a diplomatic 'nice to have'.
(b) the PRC are getting cocky now they see the US in a perceived state of relative decline. A lot of SE Asian countries are starting to look to the PRC given the US' disengagement. It serves the US well by stirring up shit like this (not that it is stirring up shit, as see point 1(a) above), as it pushes the PRC to take positions, and it flusters them, as it is a static control-led model of governance that finds it difficult to cope with change. It also points to all sorts of conflict and contradiction in their internal political discourse and external relations.
Frankly, this call is pure win.