my dad sats if you charge your phone after it us fully charged is bad?

It is true. There is little you can do, but you might be able to bring back some of the charging ability by the following:

Allow the battery to run down FULLY.

Charge until ful and immediately remove from the charger

do this 2-3 times and the battery should start holding more power longer.

You dad is incorrect. As other poster said, older style NiCad batteries had what they dubbed the Battery Memory Effect. This does not effect modern LiOn (Lithium Ion) batteries such as phone tablet or laptop. That would mean when you put your phone on to charge at night, it would reach 100% and degrade. That isn't what happens. The Batteries can show some effect from rapid charging or other occasions, but your phone knows what it is doing. When it reaches 90 or 95 percent, it drops the charging rate to save the battery and when it hits 100% it further restricts the charge down to fully off I think. Modern devices are smart enough to know what they are doing (mostly) with charging.

Your iPhone is smart enough to stop the charging when the battery becomes fully charged. It does not continue to charge and does not affect the battery in any way.

The other answers you have gotten assume you were charging a raw stand-alone battery, which you are not. You are charging a battery that is inside the phone and controlled by sophisticated circuitry that knows when to stop the charging process. What a bunch of idiots.

Older NiCd (NiCad) batteries were pretty bad for this exact memory effect, but modern lithium ion (Li-Ion) don't have it to anywhere near the same degree. You can lose some of the full capacity, but not very much.

the charger when the battery is fully charged stop to charge or "send no more electrons" to the battery.

He's not every well informed.

Don't worry about it.

This is not true for modern batteries.

depends on the battery. most new ones don't have this problem anymore