Spicey, I have been using panch phoran for a considerable time, and have never used it or even encountered it, in ground form, nor have I previously seen any suggestion it should be used that way; in what dishes would you use it ground rather than whole ?
Phil
Panch Phoran is simply a name given to a five spice mix, generally brown mustard seeds, kalonji, cumin, fennel and fenugreek it can be used in whole spice form (as you've been using) at the start of the dish or in ground form either as part of a masala to be fried at the beginning or later in the dish.
It's quite similar to Garam Masala in this sense, which can also be used in whole spice form (bay leaves, green cardamons, cassia, cloves and peppercorns) or as a ground mix.
There are no real hard and fast rules for using spices in cookery as after all we're only extracting the spice essential oils as flavouring components and these can come from spices in ground or whole form.
What you do and how you do it is entirely up to the individual, that's the beauty of Indian cookery.