High-pressure phases exist for all the ices and they're solid at quite high temperatures. For example ammonia is solid at 900 K at 90,000 bar, methane and carbon dioxide are similar. Oddly water remains a super-critical fluid under the same conditions, but up past a few GPa and it's solid at over 1000 K. Past a million bar and the phase diagrams are vague, but super-ionic solid forms are likely past 2000 K or so. In Jupiter's icy outer core it's likely to be 10,000 K and probably "solid" at 10 megabar or so. Even the rocky-iron core is probably solid at 35 megabar and 20,000 K. Pressure does funny things to phase chemistry.