Melt 1 tablespoon butter in 5-quart Dutch oven over medium. Stir garlic and red pepper 30 seconds without browning.
Add wine; simmer 2 minutes. Add broth and salt; boil.
Add spaghetti; simmer uncovered 8 to 10 minutes, stirring often to separate strands. Add reserved water gradually if drying before almost tender.
Fold in shrimp; simmer 3 to 5 minutes, turning through sauce, until opaque and 145°F, pasta tender, and some liquid still flowing around it.
Remove from heat; fold in remaining 2 tablespoons butter, lemon juice, zest, and parsley. Toss to coat strands; serve immediately.