When multiple mobile phones to be charged, they should provide a provision to chain them.
option-1) So the device first in the chain charges to 100% and then supplies power to next. once the second device charges to 100%, it supplies power to third....
Option-2) It can be reverse to option-1. Once the last device is fully charged, second from last will be charged
Option-3) All devices charges simultaneously. so the adaptor would need to supply very high current.