All chickens are carriers of Coccidiosis and this disease and others chickens may be carrying can be fatal to pheasants. There are some sturdier pheasants that can handle living in the same area as chickens, like ringnecks.
Regardless of what we all say, you are going to do whatever you choose, you seem to mix them already.
As for me, I have spent to much money on my peafowl, Golden and Red Golden pheasants to mix them in with nasty messy chickens or ducks and ducks are worse than the chickens.
Do not take me wrong, I love my chickens dearly, but between them and the ducks, until I raised them, I had never seen such filth and they are a pain to clean up from.