The phosphorus in the water is going to be most likely in the phosphate state because its the most stable one. So remember that phosphates are compounds that are insolube with all compounds on the periodic table (aside from group 1 and ammonium ions). So this is just a series of precipitation reactions.
Key things to note how to write the equations:
1. Precipitation reaction general equation is: soluble + soluble -> insoluble + soluble
2. Way to write equations in general is to know how chemical formulas work, which is just the simple case of where u switch the charges on top to give the overall chemical formula so for example in FeCl3 the iron is Fe^3+ and chloride is Cl^- therefore swap the numbers onto the bottom giving FeCl3.
3. Remember to balance equation with states as well
So you just got to apply that. Equations should go as follows:
FeCl3(aq) + PO4^3(aq)- --> FePO4(s) + 3cl^-(aq)
Al(OH)3(aq) + PO4^3(aq)- --> AlPO4(s) + 3OH^-(aq)