Prepare a grill for medium-high heat; preheat 5 minutes (or heat a grill pan over medium-high heat). Brush corn with 2 Tbsp. oil; season with salt.
Grill corn, turning occasionally, until kernels begin to char, about 8 minutes total. Let cool slightly, then slice kernels off cobs with a sharp knife.
In a large bowl, combine corn, onion, avocado, tomatoes, and basil.
In a medium bowl, combine lime juice, garlic, red pepper flakes, and remaining ¼ cup oil; season with salt and whisk until smooth.
Pour dressing over salsa and stir to combine. Serve with tortilla chips alongside.