Nowadays in America we call them pharmacists. Back when these neat tokens were in widespread use, they were called apothecaries -- people who formulated drugs. Apothecaries would use them in various sizes:

20 grains = 1 scruple = 1.296 grams
3 scruples = 1 drachm (dram) = 3.888 grams
8 drachms = 1 troy ounce = 31.1 grams

and the weights would have neat symbols on them known easily by apothecaries, but mysteries to the rest of us (they come from ancient Rome!).

The Phila stands for Philadelphia and H.T. is the short name for where it was made, that is, which company made it. Here, H.T. stands for Henry Troemner, the maker of this coin.