Is it good practice to soak PCBs in alcohol?

As Daniel as stated, IPA won’t degrade the condition of the logic board. Soaking a board in IPA will help displace the water but it’s not a magical cure-all for water damaged devices. When water gets inside a phone, there are two outcomes to consider:

1. The first is that the water will cause short circuits while the phone is wet. Where they occur is anybody’s guess but it tends to occur on common areas depending on the phone model. In some cases, the short circuits damage easily identifiable and replaceable components. In others, it causes damage to large IC’s that can be difficult to troubleshoot or replace.
2. The second is that the mineral deposits left over from the evaporated water will continue to cause short circuits, or in the case of salt water, literally eat away at the components and copper traces.

That’s why putting phones in rice doesn’t do anything. Sure, there are folks who swear that putting their phone in rice saved it but those phones would have survived no matter what was done to them, including leaving them on the counter (plus they wasted a perfectly good bag of rice ;>).

So in your case, the board has soaked enough. Let it air dry or put it in an oven at 150F or in a dehydrator if you have one and let all of the IPA evaporate. Beyond that, there’s not much you can do from a DIY perspective.