Phone chargers tend to be white/grey/black - in other words, perfectly designed to blend in with the decor in your average hotel room. Problematic when it comes to taking a final glance around the room to see if you have left anything behind - it's all too easy just not to notice your charger.
I've solved this problem with bright orange cords for my iPhone/iPad - they always catch my eye and I haven't left a charger behind since I've had them. They only cost a couple of dollars on eBay.
(Hotel rooms also tend to have power points in thoroughly inconvenient locations. I can't tell you how many times I have gashed my teeth in incoherent rage because the power points are behind the bedside tables, and too close to the floor to plug in my USB charger. The too close to the floor issue could be solved by carrying a power board, but that would just be an extra thing taking up space in my hand luggage. There is usually a power point in the bathroom you can use in a pinch.).