I am by no means perfect and have been known to spew out some pretty serious negativity of my own in the past. By taking responsibility for my actions and continuing to try to improve myself I have begun cultivate positivity and stronger connections in my own life. This amazing and ongoing transformation I've experienced makes me want to extend this feeling into all of my relationships while protecting my own positive space.
First things first I think it's important to decide what kind of role you want this person to have in your life. Negativity coming from a parent can affect you in a very different way than the same energy coming from a friend or even an acquaintance. Sometimes there isn't much of a choice as to who you surround yourself with, as with certain working or familial situations. Finding a place in your life that you feel comfortable interacting with this person is crucial. If you feel like less involvement with them would help, that might be something to consider. If this person is someone important in your life, acknowledge the weight of that relationship and begin to work on it. Obviously every situation has it's own variables and is complicated in its own ways, so you need to find what works for you. Honesty and examining the situation alone can go a long way.
If you continue to regularly interact with this person make small choices to keep yourself sane. Your mental health is a priority and if not answering the phone every once in awhile is what you need to do to keep your emotional state calm and balanced then that might be what you need to do. If you know that something you do excites their negativity make an active decision to steer clear.
Think about where the negativity is coming from. Someone who is persistently negative may be depressed and in need of professional help. Past experiences, genetics, diet and lifestyle all play a role in our ability to handle certain situations. If you feel comfortable talk to them about the source of their feelings and if needed encourage them to get the help they require.
Act instead of reacting. Sometimes a compliment or a reassuring word can be all it takes to change the tone of a conversation. Instead of waiting for a bad situation to present itself introduce something good in its place. Enjoyment can be infectious, so make the first move and start the interaction out in an uplifting way.
No matter what keep it positive. Letting someone else's negativity be reflected through you is a lose lose situation. When you get angry at their anger or frustrated with their frustration you are doing yourself a huge disservice. With every interaction you have an opportunity to aid and elevate your relationship through sharing positivity. Maybe when someone consistently complains ask them about something good in their lives or relate a similar situation you've experienced and speak with empathy and encouragement. Only you control your reaction to a situation, so be an inspiration.
“If we learn to open our hearts, anyone, including the people who drive us crazy, can be our teacher.”
– Pema Chodron