You may have to connect at LAX or SFO to get to a flight to China (where in China?). Be careful with itineraries with connections in LAX or SFO -- LAX may be slow to get from an inbound domestic flight to an outbound international flight, while SFO frequently has inbound flight delays due to weather, so allow generous connection times at either airport to reduce the risk is misconnecting your transpacific segment.

Star Alliance should give you good PHX-{LAX,SFO} options, as PHX is a US hub and LAX and SFO are UA hubs. Star Alliance also has a good selection of airlines flying to Asia.

But you may want to put PHX and whatever place in China you will go to in a flight search to see what airlines come up as choices. You may want to sign up with the airline that you will fly most of the transpacific segments on (miles and status derived from miles tend to be most beneficial on that airline, compared to alliance partners).