It turns out, if you unplug your phone charger to plug in your Silhouette Cameo, your phone can't charge. Even if you put the USB end into the phone.
So I had a dead phone this morning. I tried all my usual revival tricks, and then went down to the phone store, where the guy tried it on a different charger. It's alive! Yay!
I was prepared to buy a new one, since this one is almost 4 years old, but I didn't have to! I don't know how I feel about that now. Hmmmm.