Apple mobile phone charging using fast charge and slow charge does not have much impact on the phone. But a lot of charging will have an impact on battery life, because charging will make the battery hot, excessive heat may shorten the battery life.
The best way to charge is to use fast charge when your charge is below 20% and slow charge the rest of the time. Also, don't let your phone charge to 100%, as this will shorten the battery life. Therefore, when using an iPhone for a long time, you must carefully choose the right charging method to protect the battery.