Why won't my phone turn on?

Liquid damage is particularly concerning, as it can damage components and can even get worse over time. Given it was in the washer for that amount of time, the only chance you have to save it is to disassemble the whole thing, clean it thoroughly and hope for the best. This guide shows you what you need to do to have any chance of salvaging your phone.

iPhone Liquid Damage Repair - iFixit Repair Guide

At a minimum, you'll almost certainly need to replace the screen and the battery, both of which are particularly susceptible to liquid damage.

The alternative is to take it to a shop that specializes in liquid damage, but even they won't guarantee their repair since it can be so pervasive. Most people at this point would opt simply to recover any data they need from the phone (if possible) and retire the poor thing, but ultimately it's up to you.

It is if the utmost importance to take action immediately, as the longer you wait the greater the chance of irreparable harm to the phone. In the meantime, do NOT power on or charge the phone and DON'T put it back in rice; not only does that not work, it can make things worse by getting dust and particles stuck inside the openings of the phone. If you really feel the need to do something like that, get yourself a supply of silica gel packets that do actually absorb moisture and store the phone in there instead.