First of all, iPhone uses lithium-ion batteries, so you should follow the same advice as for the laptop batteries. Look at this and this questions at SuperUser.
The most two damaging things to Li-Ion batteries are deep discharge and heat.
Deep discharge is when you use the device until it shuts down, then wait and attempt to turn it on. That's bad practice - you should stop using the battery and think of charging it as soon as the device turns off for the first time. Deep discharge can severely damage the battery. Similar batteries are used in profesional Bosch power tools like drills and drivers. Obviously battery is a heart of such tool. When you continuosly use a tool its battery can get discarged suddenly and then the tool will shut off - you will be holding the switch pressed but the tool will just stop rotating. The manual says clearly that you shouldn't try to release the switch and press it again to try to restart the tool - according to the manual that can damage the battery.
Heat lowers battery lifetime. Heat comes from leaving the phone under direct sunlight, carrying it in a pocket close to your bode in hot weather, putting it next to a heater and so on.
Obviously you shouldn't do stupid things like piercing, burning, short-curcuiting and dropping the iPhone. All other factors like how often you charge it will have very limited impact on the battery lifetime. Even Bosch power tools manuals don't ever mention anything about how good or bad is charging the batteries often.