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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.
This means when you receive your phone it should be at 40% charge, otherwise they will have aged your battery for you. (you are probably used to the effects of aging, like a 2 year old phone seeming to have very short battery life).