Place the sun-dried tomatoes in a small bowl and cover with 1 cup of boiling water; let sit at room temperature for 10 minutes to rehydrate.
Drain the tomatoes well using a colander or fine mesh strainer, then chop them finely.
In a mixing bowl, combine the softened cream cheese, plain Greek yogurt, and chili sauce until smooth; use a hand mixer for a creamier texture or a spatula to stir.
Add the chopped sun-dried tomatoes, chopped green onions, chopped red bell pepper, minced garlic, celery seed, and cayenne pepper to the cream cheese mixture and stir until evenly combined.
Refrigerate the dip for at least 1 hour to allow flavors to meld, then serve chilled.