When someone is frustrated, angry, or upset, you want to help. You want to give advice, explain how you (or someone you know) successfully dealt with a similar situation. The best thing to do is often the hardest, especially when you're dealing with an adult child or an aging parent.
Just listen.
Offering a helpful suggestion can be a fast way to end a conversation. It's more generous to give the other person the opportunity to vocalize their thoughts and feelings and perhaps come to their own solution.
Empathize, "I'm so sorry for your troubles...." and keep listening.
You might ask, "Is there anything you need me to do to help?" But sometimes all you really need to do is care and be there.