Are you a mummy made of salt or are you a mummy that's salty about the whole dying and mummification thing?
Neither. Salt mummification is the best. Most liches have to deal with their bodies dying, rotting away, and then the constant hassle of trying to hold a skeleton together. My body on the other hand was mummified in the traditional Gulgathan manner using a salt mixture called "natron." It's a method we borrowed from the egyptians, but we usually cover our mummies in a layer of red clay as they mummify and we don't extract the organs. I just had to sit around in my little ball, wait the few months the process took, and then I could retake control and move it around. The only drawback is that everything tastes of salt.
So, wouldn't your corporeal form be destroyed by fire pretty easily? Such as that readily available from matches or found in the boiler of 19th century trains?
Yes. It's happened before. It's not so bad though, I just release the body and have one of my minions hide my phylactary in with some trinkets and treasure. Eventually some idiot will find it and make the mistake of touching it. After that, it's a slow process of destroying their mind with dreams or visions and displacing their soul. Unfortunately it does mean that I lose a lot of time. Especially if no one comes treasure hunting for awhile. The best was that wizard though. I didn't even hide the phylactary. He just wandered in to my lair looking for the secrets of life and death. He found me instead. Moron knew exactly what the little silver ball in the ivory box was right away and STILL tried to grab it. XD It didn't take much to seize control either. That was in the days before I could get volunteers though.
The short answer is, yeah. Liches are physically weak and magically strong. Destroying our physical bodies is fairly easy once you get through all the wards and protections.