On my server phantoms while phasing doesn't render as they should,causing them to see in blocks like normal,without blindness effect. List of mods and how phantoms see on server attached.

Hi. This is usually not a problem with mods on the server, but mods on the client. Any mods that alter rendering might be the cause. For example OptiFine is a prime example of a mod that causes this problem. Unfortunately there's not much I can do about it.

I had this same issue, and it turns out I had turned off the "fog" option, under video settings and details (with optifine), which is what did it.