Will taking my iPhone into the bathroom whilst showering on a daily basis wreck my phone?

The iPhone has always had a limit in its tech specs, under environmental requirements of

"Relative humidity: 5% to 95% noncondensing"

So if the water is condensing in the bathroom, then you very well could be causing condensation inside the iPhone itself, which is likely to cause corrosion or electrical shorts.

It very well could, yes. The excessive humidity generated by a hot shower could cause condensation inside the phone which can ruin it.

A little comon sense says... yes, it very well could damage your iPhone, or any piece of electronics that is not water proof or at least water resistant.