Is it too confusing for my Alzheimer's mom to talk on the phone with my dad, who doesn't live with us?

The length and frequency of your mom's conversations ought to be dictated by her demeanor. Due to her Alzheimer's, she most likely forgets within minutes that a conversation even happened, so these contacts are primarily for your father's benefit. As long as they appear to bring your mom pleasure, by all means support them. However, if she starts showing stress during or right after the call, you'll want to make changes. The conversations may simply be too long, stressing your mom's concentration tolerance. In that case, ask your father to shorten the calls or cut them back to a couple of times a week.

On the other hand your mother could be reacting to the contents of the calls. Common stressors are direct questions that challenge a person's memory. Ask your dad to avoid phrases such as: "do you remember?" Your mom most likely won't know what he's talking about in that moment, but his tone tells her that she "ought to remember" and when she can't, she may feel she's failing, causing her anxiety.

However your father can still talk about shared events. Instead of posing a question to your mom, he can rephrase it as an anecdote or a story. If he finds that one or two episodes give her special pleasure, in which case you can urge him to repeat these as often as he wants.

If you have succeeded in making these changes and she still gets agitated during or after the calls, it's time to find another way to help your father keep her in his life. This could as simple as a weekly postcard with updates or you could keep a journal with photographs and short videos, something your family will certainly treasure later on.