Cook the pasta according to package directions. Once cooked, reserve 1 cup of pasta cooking water and drain.
Meanwhile, melt butter in a large skillet over medium heat.
Stir in whipped cream cheese, garlic. Cook it for about 2 minutes, whisking occasionally. (Note: The mixture will look curdled and weird, but don't worry, it's totally normal.)
In 2-cup measuring cup, combine heavy whipping cream and milk and slowly stir into the cream cheese mixture, whisking constantly.
Bring the sauce to a boil, stirring occasionally.
Stir in parmesan cheese and continue to cook until desired thickness. (Keep in mind the sauce thickens rather quickly. If the sauce had thickened too much, thin it out with a bit of pasta cooking water.)
Add cooked pasta, smoked salmon, parsley and lemon juice. Toss everything until well combined. Serve immediately.