I was tricked into a mouthful of phal many years ago by my father. He thought it was hilarious seeing my reaction. I couldn't taste the rest of my curry, but at least he was paying. My Dad would look extremely uncomfortable eating his but assured us he was enjoying it. He no longer has the hot ones any more. I happened to go for a curry with him last night and he had a madras.
Personally I normally go for the tandoori dishes like a sashlick. When it comes to curry I go for taste over heat. Having said that, I can eat a lethally hot chilli con carne and I can still taste it.
Years ago, an indian friend of mine told me that "phal" means "ridiculous" in gujarati. Her theory (which I subscribe to), is that drunk Brits would stagger into a curry house late and all try and outdo each other. Once they'd all got used to Vindaloos, they starting asking for something hotter. The first waiter to be asked for one told said drunks half jokingly said they have one called a phal which is hotter than a vindaloo. The drunks went ahead and ordered it. Repeat orders (to not lose face) meant it ended up on the menu and then spread to other curry houses in town, then further afield.