Double Phoenix is a mark used by the Nihon Koshitsu Toki Company (NKT) in Japan.
They started production in 1908, moved to Korea in 1917 and moved back to Japan in 1961.
The company is now called Nikko China. Patio is the pattern name. Replacements doesn't date the pattern.
You can guess at the age because of how the country of origin is notated, but it's not reliable.
In 1890, the US passed a law that said imported items had to be marked with the country of origin. In 1914, the law was revised to include the words "Made in."
So, my "educated guess" - without actually seeing the backstamp and spending perhaps hours researching it lol - is that your china was made between 1908 and 1914.
Hope that helps.