Sorry but ice giants aren’t unique in having a liquid interior, gas giants do also, and in fact below the liquid H/He ocean there will be more phase transitions, with a solid, metallic phase of hydrogen at the bottom, and then a core probably made of diamond, or at the very least all the rocky and other heavy stuff that will have sunk down there over its history.

The name ‘ice giant’ is one of these stupid astronomical naming conventions that makes no sense to the rest of us, specifically ‘ices’ means ‘volatile’ chemical compounds like water, ammonia and methane, and an ice giant is composed primarily of elements heavier than H/He, but they won’t actually be in an ‘ice’ form like what we put in our drinks, as you say, there’ll be liquid oceans once the pressure gets high enough.