When I was a PNAM (oh, just a scant week or so ago)
, I attended another organization's local founder's day celebration. It was held at a (large and stately) home of one of the alumnae members. Tea and coffee were served, along with sweet and savoury snacks, and a couple of desserts. It was a lovely event, and because it was in someone's home (as opposed to a restaurant or club) a few of the members remarked that they enjoyed it a bit more.
I haven't attended an Alpha Phi founder's day celebration, but according to my sponsor, they have a tea either at someone's home or a restaurant.