Acceptable charge current somewhat scales with cell capacity, all other details being equal. This may not be entirely true (if you are generating heat, smaller cells can potentially better dissipate it due to their lower volume-to-surface ratio) however it is true enough that we generally speak of charge rates not as an absolute current, but rather as a fraction of the cell hourly capacity, or "C". So for example a ".2C" charge rate would be charging the cell at 20% of its rated capacity per hour. Given that there are inefficiencies and you have to slow down as a delicate lithium chemistry nears its voltage limit, this .2C rate might take at least six, maybe seven or eight hours. In practice, based on external measurements I think my phone will charge at more like .3C, and I have small cells for RC flying machines that are engineered for high discharge rates and can be charged at over 1C. Whatever the "C" rating, two small cells would charge no faster at it than one larger cell of the same C rating having the same total capacity.
But there's another issue in many phones: the USB spec limits supplied current to 500 mA. This is more limiting than what the cell can tolerate as a charge in most cases today, so it is common to build chargers with sense resistors or other tricks on the data lines so that the phone can identify that a special charger is present and charge at a higher rate. Unfortunately, the way they do this hasn't fully been standard - though there are attempts to make it so today, it is still quite possible you might get a mismatch between charger and phone forcing a fallback to a 500 mA or 2.5 Watt charging rate. In the past I often found an outlet-plug wattmeter useful to tell if a charger was charging a device at high rate, or only at USB rate - the reading would include losses in the charger, but the different between seeing a 2.x watts vs seeing 6 or 7 display is significant. Today you can get inline USB current meters which would also work, at least if you get one that connects the data lines through.
Your needs may ultimately be met by the new USB fast-charging standard which is intended to get you a useful fraction of capacity in a short period of time - until then make sure that you are charging your devices at their designed maximum rate, and not through mismatched chargers or bad cables at the fallback 500 mA one.