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I tend to agree you with you in that this is an efficient and reasonable use of time within reason. An executive level position is going to require more than just the 9-5 schedule and carries a greater responsibility. With that said, there is a time and place to take these phone calls and send emails. If you are constantly getting up from dinners or interrupting family time in the evenings or on weekends then she may be viewing this as an invasion of your privacy and family time.
In my profession, I face the same responsibilities and often have to respond in the evenings and on weekends. Since many of these messages do not demand an immediate response, I would recommend coming to an agreement with your wife that you set aside a specifice time period in the evening and/or weekend and just do all of your out of the office work in that time slot. This compromise will allow you to be efficient outside of the office and offers your wife some structure in that she knows you will only be addressing work during that specific time period.