please help - can iphone break chargers

Hi, in the past 3 months ive bought 5 charges and all seem to stop working between a week to 2 weeks. They either stop working overall or only work in specific positions and keep making the vibrating noise due to it only woring in very few positions. The adapter is in good codition and works perfectly and ive tried several wall sockets so the only cause seems to be somehow the phone. I dont bend on the charger or use it agrresively or pull on it hard when i use it and there never seems to be visible damage to the cord at all. Please help!