That sounds like it would be pretty disruptive to your family life. It might just go away on its own but if the fear is increasing you probably need professional help to do a desensitization process correctly. ABA would be helpful with this but if that's not an option, try to find a therapist who specializes in cognitive behavioral therapy that has experience with autism. The sooner you can get this under control the better because the longer it goes on the more entrenched the become and the harder it will be to modify.

I don't have this problem with my ASD son but rather I myself *hate* the phone ringing.
For me, I believe it is the sheer randomness of it. I can't predict when it might ring and that really bothers me. But I am an adult who has gone through various therapies so I can cope. We also got newer phones that plays musical tunes rather than a ring, which is less annoying.

Thank you for your answer I will talk to our ABA therapist and hopefully she can help! Thanks for the help!!