Does she interfere with the running of the household? Do you have weaknesses that he sees clearly (as a man) but which your mum cannot see (as a mother)? There must be a reason for this - like someone pointed out,iko kitu and perhaps you are not telling it all as it is. I personally would prefer the least interaction with a mother-in-law I do not get along with....I'd steer clear of the phone,the house,etc. There MUST be something - either he feels she is running your family's affairs (by telling YOU what to do and what not to do,what the kid should wear,who to visit,who to be friends with,etc). Basically he might feel that he has married her and you are just a proxy.
The problem with equality is that we desire that it be with those that have more than us rather that those that have less