arrange the given bonds in the increasing order of polarity:
P-H, H-O, H-F, N-H

Dear Student,

Here H is constant while the other element is changing. 
Now, we know that as we move along the period, electronegativity increases and down the group electronegativity decreases. Therefore, the order of electronegativity of these elements is:
F > O > N > P
Greater the electronegativity of the other element, greater will be the electronegativity difference and thus higher will be the polarity. Therefore, the increasing order of polarity is :
P-H < N-H < H-O < H-F