Into a measuring cup, drain the canned clam juice. Add the bottled clam juice until you have a total of 2 ½ cups. Set aside.
In a large pot or Dutch oven over medium heat, add the bacon. Cook until crispy, about 8-10 minutes. Transfer to a paper towel-lined plate, reserving 2 tablespoons of bacon grease in the pot. Discard the excess grease.
Add the butter to the pot. Once melted, add the onions and celery. Stir and cook until softened, about 5-7 minutes. Add the garlic and cook for 1 more minute.
Sprinkle in the flour and stir to coat the vegetables. Gradually add the chicken broth, reserved clam juice, potatoes, parsley, oregano, salt, black pepper, and red pepper flakes (if using). Stir to combine.
Bring the mixture to a boil. Once boiling, reduce the heat to low and simmer until the potatoes are tender, about 12-13 minutes.
Stir in the heavy cream, chopped clams, and most of the bacon, reserving a small amount for garnish. Simmer for 2-3 minutes, or until everything is heated through.
Ladle into bowls and garnish with the remaining bacon and chopped parsley. Serve warm.