Melt two tablespoons butter in a large, high-sided skillet over medium heat. Season chicken thighs with garlic powder, salt, and black pepper, to taste, and add to the hot skillet.
Brown the chicken thighs on each side, approximately 3-4 minutes per side. The chicken should release easily from the bottom of the skillet when ready.
Transfer chicken to a platter and add remaining butter to the skillet. Add the sliced Portobello mushrooms and sauté, stirring occasionally, until the mushrooms develop some color and start to release their liquids, approximately 4-5 minutes.
Pour the chicken broth into the skillet and gently scrape up the brown bits from the bottom. Return the chicken thighs and that collected on the platter to the skillet.
Reduce heat to medium-low and cover. Simmer until the chicken is cooked through, approximately 25-30 minutes. Remove pan from heat and transfer the chicken to a platter. Cover and keep warm.
To prevent curdling, temper the heavy cream by adding one or two tablespoons of the hot liquid from the skillet to it before adding it to the pan. Add the cream cheese to the skillet and stir until it is thoroughly melted and incorporated into the sauce. Taste and adjust seasonings, as desired.
To serve, spoon some of the pan sauce and mushrooms over each chicken thigh and sprinkle with some fresh parsley, if desired. Serve immediately with your choice of sides. Enjoy!