The name of this place alone screams mediocrity and, indeed, it was mediocre (at best).
I came with some family and friends at 2 p.m. on a Saturday. The restaurant wasn't very busy, but after getting a table, a server didn't come back to check on us for a good ten minutes. In fact, we never even received menus; to speed things up, we grabbed some take-out menus on our own, because it was clear things were going to be slow.
It took another 30 minutes for any food to arrive. I was in a group of 6 and only half the group got any of their items; the other half had to wait another 15 minutes for their orders.
But forget the terrible service. How was the food?
I got a Thai basil stir-fry with tofu ($9) and brown rice. One thing Thaiphoon does right is to offer a nice variety of brown rice. Other than that, though, the food insipid: watered-down, bland, generic soy-sauce stir-fry with plasticky Sodexho vegetables. No options for mockmeats (or even seitan).
As with most Thai restaurants, many of the "vegetable" dishes contain fish sauce, so make sure to ask about that. Their curries, too, contain shrimp paste and cannot be modified, so if you're vegan or vegetarian, don't order the curries at all.
Thai food in the US generally is low-grade and watered-down, so I usually don't have high expectations. Thaiphoon fulfilled my low expectations food-wise, but dropped even further with its slow, erratic and inattentive service.