No, phase-change materials are NOT viable alternatives to chemical energy storage. As an example, look at the heat released as water goes from a gas to a liquid. If you could capture and use all of that energy (which you can't), there's still only about 92 Wh/kg available there, and that's with ignoring the mass of any machinery.
Telsa's chemical storage bty's are about TRIPLE that theorical value, and that's a real-world product with demonstrated 80%+ round-trip energy efficiency. If there was a better 1st-principles solution in the world of chemistry or physics, you can be confident that Tesla would already be doing it.
Pumped hydro storage is a better alternative for large storage projects than phase change materials, but even they are still no where near as efficient as Tesla Powerpacks for grid/home applications.