I come from a time when batteries weren't as smart as they are today. There were all sorts of secret tricks and rules you'd have to know, or you'd kill your battery. You couldn't recharge a battery until it had fully discharged; otherwise, you'd limit the battery's capacity. Later years brought batteries that had to be "trained." Fully discharging and recharging multiple times.
Today's modern iPhone batteries are different. There's none of that to worry about. Charge your iPhone whenever you want. In the car? Charge it. Sitting at your desk for 10 minutes? Charge it. In fact, the only real trick to remember is to make sure the battery doesn't get too low. A study by Cadex found that many Li-ion batteries fail due to being over-discharged.
Your smartphone battery - like your smartphone itself - performs best when it's charged. There's no need to keep it at 100% all day, every day. But there's no reason to let your battery level fall into the red, either. Giving your iPhone a few minutes of power will do more good than harm, so go ahead.