Bring a large pot of salted water to a boil and cook the linguine according to package directions; drain and keep warm.
In a large saucepan over medium heat, melt the butter until bubbling.
Add the smashed garlic cloves and sauté in the butter until softened and fragrant, about 1–2 minutes; remove the garlic with a slotted spoon and discard.
Stir the chopped parsley into the butter.
Whisk in the flour until fully incorporated and cook for 30 seconds to 1 minute to remove the raw flour taste.
Slowly whisk in the half and half until smooth, then add the chopped clams and the juices from 2½ of the cans.
Add a couple teaspoons of freshly squeezed lemon juice (adjust to taste), then cook over medium heat, stirring, until the sauce is hot and slightly thickened, about 3–5 minutes.
Toss the cooked linguine with the clam sauce to combine and serve immediately.