You cannot know the frequency of a signal if your only knowledge is its frequency. The frequency is defined as the first derivative of the phase with respect to the time, or: f = dphase/dt. Then if you know the frequency you will know the increment of the phase with the time, but not the absolute phase.
To know the absolute phase you must know, or go back, to the origin of the time axis and also you have to refer it to a sin(x) or cos(x).
Another thing you can define is the relative phase between two signals (explained by kak111).