I found that after a lot of usage, and accidental tugging and yanking, that my iphon charging cord was becoming damaged were the cord runs into the plug head. My first inclination was to use regular black electrical tape to fix the problem, but I hate now the stuff leaves sticky residue and tends to slide around.
I was digging around in my mess of a tool chest looking for electrical tape when I found my plastic spool of teflon plumbing tape.
I found that it is easier to cut off a length (about 6-8" of tape) rather than wind it with the spool. The tape seems to hold well and the clinginess keeps it from unravelling.The white also keeps it looking clean and neat!