You don't need to be concerned with overcharging with modern smartphones. However, if you would like to slow down the charging rate of your phone. You can use a lower amperage charger. For example, when I plug my phone into my laptop it takes significantly longer to charge the phone.
That being said the major sources of battery life decay occurs from heat and charging it from empty to 100%. Recent research shows that fast charging doesn't necessarily reduce the battery life of your phone compared to heat. For example, do not charge your phone and leave it under your pillow. Those phone batteries get hot.
Also, If you keep your phone from going below 20% it will go a long way in preserving battery life.