Brain fog is a real cognitive dysfunction issue. I got advice from a doctor:
Pace yourself and if you're not up to it, honor that and rest.
In general: Eat well, hydration, pace, take care of yourself including stress relief, reduce or eliminate "doom scrolling", all of these things and more can help support you conserving energy including in your brain. Don't multi task.

From my own experience: set a timer and let the person know you can only talk for ___ amount of time and then stick to that.
If you have a phone call for an hour, for example, and then afterwards including possibly the next day you feel extra tired, achy, unwell, next time you have a phone call only talk for 15 or 20 minutes and see how you feel afterwards.
During a phone call, lie down, feet up, eyes closed.
This can feel awkward but I had a friend who watched a lot of news and would like to relate to me what she saw about disasters, bad news, alarming news, etc... I think it was a way for her to just process the stress she felt. I would say something supportive but then change the subject. I finally did ask her if we could have a disaster free catch up, I said it very gently and made it a "me issue" in terms of my own mental health. But really it's an energy draining kind of experience when. you care so much.

I keep a dry erase lap board or paper and pen close by during calls. 🤷‍♀️

I tell myself to just focus on the conversation, that usually helps me.

I can’t really. I talked on the phone too long. I start sweating. If I’m having fiber fog, it’s better that I put it off to another time.

Excellent advice that you shared Anne. But really thank you too everyone for your advice. A little time ago my fog was so bad it was hard for me to comprehend anything, so I understand. I've experienced years of it. It was frustrating,maddening, upsetting. I received similar advice as did Anne and I found it helpful. Another piece of advice I can give is try to remain calm during your conversation. It is so easy to become overwhelmed and if that happens all bets are off. Remember it's ok to give yourself grace and try to calmly explain to someone that you are not at your best and may need more time. Its ok to take good care of yourself. What I have to remind myself is am on being on my side. If I am overwhelmed I'm likely not on my side💕💗thanks for sharing this. I wish the best for everyone ☯️☯️☯️