It sounds like your mom means the world to you. She doesn't have to be your biological mother in order to be important to you. I can understand why you would care about her and want to make sure your relationship with her is strong. It's also natural for children to worry about their parents and wonder how they would get through life without them. The problem is that excessive worry can impair your ability to function and enjoy life to the fullest. Do you worry about other people when they don't answer their phones, or just your mom? Do you worry about other people when they're driving, or just your mom? Do you worry about people leaving you after arguments, or just your mom? If you ONLY worry about your mom, then you might want to start addressing those thoughts when you begin to have them. For example:

Action/Event: Your mom doesn't answer her phone.
Belief: You begin to feel anxious and start worrying about what could have happened to her, perhaps assuming the worst (that she's intentionally ignoring you or was in an automobile accident).
Consequence: You can't think about anything else and feel physically/emotionally exhausted until you hear back from her.

This is called the "ABC" model (Action/Event, Belief, Consequence). When this happens, you can challenge or dispute your belief and experience a better consequence as a result. For example:

Action/Event: Your mom doesn't answer her phone.
Belief: You begin to feel anxious and start worrying about what could have happened to her, perhaps assuming the worst (that she's intentionally ignoring you or was in an automobile accident). You stop, take a deep breath, and begin to think of other possibilities. You conclude that your mom is probably just busy and will call you back later on.
Consequence: You relax and go about your day. You might call her the following day if you haven't heard back from her by then, but you don't stress out in the meantime.

See how you can address your worries by taking a slightly different approach? I know this can be difficult to do in the heat of the moment, which is why it's important to practice this technique until it becomes easier for you to challenge or dispute your beliefs! =)