In typical wirings those have all same wire thickness (there are some special cases where different size wires are used for different wires) and they generaly go together the same route from the electrical power supply to the load.
Differences:
The ground wire is designed not to carry any current in normal operation (soem small current can flow in it due leakages in the system insulation and due capacitive coupling). The ground wire will carry considerable amoutn of current only in case of system fault for a short time (typically the time it takes the fuse to blow or other protection device to trip).
Phase and neutral wires are designed to carry the current needed for the connected electrical device (the load) to operate.
Phase wire will have the full mains voltage on it and the full current.
The neutral wire will have just a very small voltage (typically few volts) on it, but still the full load current is fl
