I'm a beginner: If the mobile phone charger has two USB ports for output and the charger is labeled 4.8A, does it provide 4.8 maximum to both ports or to each port when cables and mobile phones are connected? If only one cable and phone are connected, what is the maximum output? How does it affect the speed of charging? Is there a splitter or simply a joint in the wiring?
If there is a single label, it indicates the output of the whole charger. Hi-power chargers usually also specify max current per port because a USB connector has its own limit. 4.8 A may be too much for a single USB port even if the adapter can provide such current. Normally, current of a standard USB port should not exceed ~2A, see What is the maximum physical current that can pass through a standard USB cable?
Speed of charging will also depend on the quality and state of the cable and connectors, and whether the device and the charger both support a fast-charging data protocol.
Ideally, if the total current draw does not exceed the limit, multiple connected devices should not affect each other.
It provides 4.8 amps to both ports. If only one phone is being charged at a given time, it will provide 4.8 amps to that port alone. As far as the wiring inside of the charger goes, I am not sure. You may want to try to find a datasheet on one of them online.