Let the balancing coefficients be a,b,c,d. a before p2i4, b before h2o, and so on.
next, balance for all the atoms,
like to ensure the no. of P atoms on lhs and rhs of the equation,
for I atoms,
for H atoms,
for O atoms,
next, find relations between all the coefficients, let them be all in the form of a, say.
solving those equations, we have,
a will get cancelled on all sides.
convert the coefficients into natural numbers.
the equation is balanced now.
ask if you still have doubts..