Chemical Kinetics Problem Seen Before

The reaction of formation of phosghene from $\ce{CO}$ and $\ce{Cl2}$ is $\ce{CO}+\ce{Cl2}\rightarrow \ce{COCl2}$. The proposed mechanism is as follows:

$\text{(i) }\ce{Cl2}\xrightarrow [ K_{ 1 } ]{ \xleftarrow { K_{-1} } } \ce{2Cl}\quad(\text{fast})$

$\text{(ii) }\ce{Cl}+\ce{CO}\xrightarrow [ K_{ 2 } ]{ \xleftarrow { K_{-2} } } \ce{COCl}\quad(\text{fast})$

$\text{(iii) }\ce{COCl}+\ce{Cl2}\xrightarrow { { K }_{ 3 } } \ce{COCl2}+\ce{Cl}\quad(\text{slow})$

What is the order of reaction?