Hey I am/was having the same problem. Every time I would launch the default Phone app on my Droid X it would attempt to open, crash, then take me back to my Home screen. Downloaded Dialer One which works perfectly. However, I have not been able to make Dialer One my default phone app so I wanted to find out the solution to this. I also just re-flashed my phone with the new .sbf (gift2) and my phone is running GREAT except for this stock phone app issue. I read above that changing LCD Density may cause phone app to crash. Sure enough I have LCD Density changed to 175. Changing this back to 240 resolved the phone app crashing problem!
So, for whatever reason, the LCD Density being changed to 175 causes the stock phone app to crash...at least on my Droid X.
Going to write developer.
Anyone else having this problem and/or have a fix?