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No, not necessarily, but it can cause a minor issue. iPhones use a Lithium-Ion battery for its power, using while it's charging won't necessarily ruin the battery, but if you're using the phone while the battery is in the charging process, it can cause the phone to think it has more power than it actually has.
Your battery life will last longer if you keep your phone charged between 40% and 80%. The truth: Your phone may be a machine, but it still needs to take a few breaks. An Apple Genius said that in order to maximize battery life, you should turn off your phone from time to time, especially when you go to bed at night.