Comment by jjk166
When was the last time your phone stopped working due mechanical PCB damage?
Typically the limiting factor on your phone is the screen breaking, your battery life getting too short, wear and tear on components like buttons or the charging port, and factory defects. Epoxy isn't going to help with any of those. The only thing it would help with is exposure to water, but if other parts of your phone like your screen aren't water proof, what's the point?
Epoxy adds weight and manufacturing cost. It introduces design challenges as you need to balance the thermal expansion of the various parts. It's an extra step that can go wrong, and makes repair of other defects far more difficult. What benefit is there for the typical consumer that outweighs these costs?
To add to that. My son got his phone caught in a reclining chair without realizing it. The fact that the phone bent in half instead of destroying the chair is a nice bonus. Replacing the phone was cheap, replacing a chair would not have been — yes, both are insured, but replacing/repairing a chair takes a hell of a lot longer.