Whisk together the broth, flour, tomato paste, onion soup mix, 1 teaspoon salt and 1/2 teaspoon pepper in a medium bowl until combined. Add to a 6-quart slow cooker and top with the mushrooms and chicken. Cover and cook on high for 4 hours.
When ready to serve, bring a large pot of water to a boil; salt the water generously. Add the noodles and cook until al dente according to the package directions. Drain and toss in a large bowl with the butter until the butter is melted and the noodles are completely coated.
Transfer the chicken to a small bowl and shred with 2 forks. Whisk the cream cheese into the sauce until completely incorporated; stir in the chicken and noodles. Top with parsley before serving.
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