First off, don't set the cat up for failure -- if you know he chews on your phone charger cord, don't leave it out unattended.

Put away ALL CORDS, or limit access to them.

Secondly, try a "bitter chew" or "chew deterrent" spray found at any pet or general goods store. Spray it on a paper towel and use it to wipe down any and all exposed cords that he may have access to.