if your question is "why does the [phasor~] signal need multiplied by differing amounts in order to drive [play~]" then the answer is simple. The [phasor~] is outputting a ramp from 0. - 1., [play~] expects a signal representing millisecond playback, therefore the 'raw' (0-1) signal from phasor would only play the first millisecond of any file. Multiply the ramp by 500 and you will hear the first 500ms of a file.
Divide 1000(ms) by the length of your file (in ms) to give an appropriate frequency value for the phasor: