I also put my Razr in a ziploc, along with my wallet and some other supplies, and have not had it fall out in many years of carrying phones in the jersey. If it seems too loose in the pocket, I might put the ziploced phone into a little cloth drawstring baggy (like a Crown Royal bag) for some extra friction.

That said, I HAVE had my Crank Bros. minipump jump out of my jersey pocket on a bumpy, fast section (25-30 mph) of mild downhill when I was in the drops. I'm not really sure why it jumped, since I ride this section hundreds of times over the years. A few cars ran over it, but I went back to retrieve it. I had to file off some gouges, but I still use it, and I still just slip it into my jersey as usual.