The problem is that conversations like this usually don't work if you start with criticizing his mother or his behavior. Your husband will hear an attack and put up his defenses, and things will only get worse. Try to frame it through your own feelings and needs: "I feel like I'm not a priority in your life. When your mom calls ten times a day and you listen to her more carefully than you listen to me - it hurts. I want us to have a family where we make decisions together, not your mom." It sounds softer, but more specific. The key thing is to talk about yourself, about how hard it is for you, not about what a bad son he is.
After that, you'll need to work out boundaries together. Maybe some of the calls can be moved to the evening? Maybe he'll check with you before agreeing with his mom's opinion? It should be a solution you both came up with, not rules you imposed on him. Keep in mind that this might be harder than it seems - these patterns often go back to childhood, and he himself might find it hard to change. If talking doesn't help and things keep getting worse, it's worth thinking about getting help from a family therapist. It's not about anyone being at fault, it's about finding a normal balance.