Melt butter in a large deep skillet or pot over medium; cook garlic and pepper flakes about 1 minute until fragrant without browning garlic.
Cook shrimp 2-3 minutes per side until pink and cooked through; set aside on a plate.
Add broth, scraping up browned bits; bring to a boil.
Halve pasta; add to boiling broth and cook 8-10 minutes, stirring occasionally, until almost tender.
Reduce heat to low; stir in cream and Parmesan and cook 2-3 minutes until sauce thickens slightly.
Return shrimp; add lemon juice, toss, and cook another minute to heat through.
Season with salt and pepper; garnish with fresh parsley and serve immediately while creamy.