She is a toxic parent.
Boundaries are needed and it will take a while for her to understand that her son has erected walls.
When she calls. Do not answer the phone. Let her leave a message or voicemail. Then, if needed, call back after a self imposed 24-48 time period. Let her know she is not of vital importance and that she has been downgraded from MOM to PITA.
She can do these things because her children give her permission to do them.
That’s a really good point; your husband has played his role in this ongoing drama by continuing to participate in it. It is possible to cut a parent out of your life completely; it is also possible to strictly limit your interactions with them to what YOU can handle. At 25, your husband has his share of the blame for continuing to allow his mother to poison his life.