Since you used your money and the money they gave you to buy the phone, you could have tell them the truth and avoid getting beaten, i mean they will understand and even praise you for using your money wisely rather than using it for junks, another mistake was not telling them you bought a phone.
It was an experience that I will never forget. For the fact that I bought the phone is enough reason to get punished not to talk of buying it with part of my money for feeding. I will go hungry for it. That was how strict my parent was then but today I commend them for job well done. It thus shaped my life