I have flight China Southern from London to Manila with stopover in Guangzhou and Sanya...

It depends on how long your stopover is. If it’s less than 24h, no visa is needed. If not, you need to get a visa in advance.

Hi, I will fly from London to bali via sanya and Guangzhou on a southern China airline. As my overall stopover will be less than 24h do I need a visa? As it shows as only stopover...Do I have to disembark or maybe even change terminal ? If I need a visa where do I go make it? Is it free? I hope u can help..thanks

Of course you need to disembark and change terminal. And you don't need a visa because you are eligible for 24 hours free visa.