My phone falls in my pool... How do I fix it?

I dont know how similar you model is to THIS but you need to get the phone open and dry ASAP to avoid further damage.

You should also look at this guide to water damaged electronics

Was it a salt water pool? If so the salt will cause corrosion very fast so time is of the essence.

I used to repair 2-way radios that were dropped into sewers by repair crews... The standard procedure was tell them to take out batteries and put in a bucket of clean water and bring to us ASAP. We would then disassemble, wash with distilled water, alcohol, and dry in an oven at around 45C. Usually did the trick

If possible get it open and battery removed and wash it down with alcohol and dry it. leaving the batter connected will likely mean additional damage as corrosion/salt causes shorts on the electronic components, boards etc.

Some report success putting device in a jar of rice to absorb the water but this doesn't address corrosion issues now or in the future.