Is a wife entitled to ask her husband to reduce his daily phone calls with his mother, especially with their upcoming travel, and what should she do to avoid negative feelings and sin?

You are in a great blessing as long as love is present between you and your husband and respect prevails between you and your in-laws. To preserve this blessing, you must thank Allah Almighty for it, for He said: "If you are grateful, I will surely increase you [in favor]." It seems you are overly sensitive, and what you mentioned about your husband's mother calling him and him informing her of some matters does not indicate interference in marital privacy. You do not have the right to ask him to reduce these calls with his mother, as he might intend to honor her by doing so. Your husband should consider what is in the best interest; not everything known should be said. You should turn away from thinking about your husband's relationship with his mother and consider it something that does not concern you much, based on the Prophet's (peace be upon him) saying: "From the beauty of a person's Islam is his leaving alone that which does not concern him." Know that Allah Almighty may open many doors of goodness for your family due to your husband's dutifulness to his mother.