Any conductor can be used as an antenna and will radiate or capture some RF. As with many other situations in life there are times when a less than ideal design is used because many other factors have to be addressed. The cell phone antenna is one of those situations. It is likely that the antenna is simply the way it is because it can't be any bigger. It may be far from a good antenna at these frequencies but as I said above, any conductor will radiate RF. The cell phone itself has the circuitry to deal with this shortcoming. As Nigel said - they make up for the shortfalls with more power or increased receiver sensitivity. It also has circuitry to protect the transmitter from the gross mismatch and the changing mismatch that is the result of changes in position, proximity to other things, etc. None of that makes the antenna better - electrically the antenna might be a poor design but it's the best that can be done under those circumstances.