Phuket - Shanghai - Phuket

Unfortunately, your itinerary is not eligible for 144 or any other visa free transit option. As you can see, this is a simple return journey that cannot be considered as a transit.

You have to understand just one detail... The immediate points before and after your Chinese destination have to be in two different countries or eligible territories (eligible territories are Hong Kong, Taiwan and Macau). In other words, with some creativity, you can become eligible by introducion a third country / territory... For example:

Phuket - Shanghai - Hong Kong - Phuket

The above itinerary is eligible because it has immediate points before and after Shanghai in two mdifferent countries / territories. So, try to adapt your itinerary. Otherwise, you would have to obtain a Chinese visa in advance.