The line with the bolt represents the time the phone was on the charger. The phones try to extend their battery life by not overcharging. Overcharging makes batteries degrade faster. This is also why phones have the option to only charge up to about 80% during times you’re less likely to need it. For example, if you normally get up at 8 AM the phone will wait till about 6 or so to charge past 80%. This is because it takes more energy to bring the phone up to 100% during those last 20%.

If the phone is at 100%, then it no longer needs to charge the battery and can simply use the electricity from the charger to do its functions.