I believe that no harm will come to the phone, battery or charger if you use the phone while it is charging. I do so regularly.
It is regarded as bad practise by certain experts to allow the battery to discharge to less than about 40%, or to charge it to a higher level than about 80%. However, I suspect that very few owners concern themselves with such matters, and, like me, charge to 100% and recharge when convenient....although it is certainly regarded as unwise to allow a battery to discharge fully.
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