Why Chinese phones are cheap?

One of the most common reason why Chinese phones are cheaper is because of easy availability of labourers at low cost. China has lowest labor costs in the world and this is the main reason why a lot of manufacturers build products there

Chinese manufacturers prefer selling products on e-commerce as it is the booming technology. Companies like Samsung and Apple have spent it’s fortune in building their own stores. So basically when you are buying a Samsung or Apple phone you are not only paying to the company but its distribution and it the cost of running and maintaining the store. Chinese phones are cheaper as it is not of one specific brand and does not have a physical store.
Another factor is that Chinese manufacturers aren't packing their phones with the very latest and greatest hardware. They're more interested in balancing price with performance. If you've ever browsed a website that sells Chinese smartphones, you've probably seen devices that have reasonably high-end specs, but cost a lot less than a Samsung Galaxy S6. The Galaxy device uses higher quality parts, which are also more expensive.
Chinese manufacturers generally have a very low profit margin for smartphone sales, so they often resort to selling accessories to increase this margin. The most common accessories are phone covers, but some manufacturers, such as Xiaomi, even sell shoes and slippers.

In many cases, Chinese manufacturers choose a Mediatek processor, which might not be up there with Samsung's Exynos units, but is a lot cheaper. Plus Mediatek is also a Chinese company, so it can offer cheap local distribution.

These are the causes why chinese phones are so cheap