I’m at a loss. What options do I have when the behaviors of other students in the class impact the diagnosis of my kid (worsen anxiety)?  It’s mostly disruptive behaviors of other kids as opposed to safety concerns. 

First, you would need to show that the behaviors of other students affect your child's ability to access the general curriculum due to his disability of anxiety.  I don't know if you have an IEP or a 504 Plan, but maybe ask the school district to do some observations of him/her in class, hopefully catching a time when disruptive behavior is taking place and providing an opportunity to see how your child reacts.   You should also have conversations with your child after school each day and document in a journal times that he feels anxious and is unable to participate and learn in class.

Second, make sure (whether in the IEP or 504) the necessary accommodations are in place for his anxiety.  When disruptive behavior (or anything) causes anxiety, does he have a "safe place" he can go to?  Can he ask for breaks?  If he falls behind in class due to the inability to participate and learn or having to leave the classroom, is he provided with any kind of "catch-up" instruction for what was missed - either in special education classroom or by the general education teacher?

Bottom line:  you need to show his anxiety (which specifically occurs during incident of disruptive behavior in the class) is obstructing his access to the learning environment.  Then you need to ask for accommodations to help him/her know the options available for dealing with this AND how to keep him/her from falling behind when those options are used.

Is this in the general ed classroom?