Thank you for your answer, melloyello.
According to the website, it says 3.7 volts for "battery rated voltage" so I believe it is 3.7v device.
Ohm makes me really confusing when it comes to choosing a cartomizer, but now I understand lower ohm (2.4 - 2.6 ohm) works better than higher ohm (2.6 - 2.8 ohm).
I have used and am using fluxoes before and it works wonderfully. However, I was wondering if Top coil Phoenixes are different and since I have never used bottom coil, I also was wondering if it works better (performance, vapor production, better taste, etc)
The lower ohm atty/carto/clearo aren't better per se... what you were being told is that at the voltage you are using they are likely to be better on average, but everyone will differ slightly and you may find that you prefer a different power level. Ultimately what wattage ( power ) you like is what is important and that is what the combination of voltage and ohms tells you.
The following numbers should show you a bit on how voltage and ohms can vary and actually end up with the same wattage output.
A 2.4 ohm coil on 3.7v will produce 5.704 watts of power at the coil
and a 2.6 ohm coil on 3.851v will produce the same 5.704 watts
and a 2.8 ohm coil on 3.996v will produce the same 5.704 watts
Now let's work the numbers a different way... I'll keep the voltage the same and only change the ohms...
The 2.4 ohm coil on 3.7v will produce 5.704 watts of power on the coil as I mentioned earlier..
The 2.6 ohm coil on 3.7v will produce 5.265 watts at the coil
The 2.8 ohm coil on 3.7v will produce 4.889 watts at the coil.
Now for a bit more on this... There are several types of PV's ( personal vaporizers )... some are unregulated and some are regulated. The regulated ones also have a few types... some regulate to a fixed voltage ( an eGo as an example which is 3.3 or 3.4v ), some have a variable voltage ( Lavatube, Provari as two examples ) and some have variable wattage ( Darwin and the Kick as examples ). The most common are the unregulated ones that just run directly off of the battery. and these are often refered to 3.7v mods since that is what their lithium battery ( if they use that type ) are refered to. A fully charged 3.7v lithium battery is actually at 4.2v and when they are empty... they are at around 3.3v.
If your PV is unregulated... then when it is fully charged you will have more power at the coil ( higher wattage ) and as it drains it gets weaker and a lower wattage when nearly depleted.
I hope that wasn't too much info... but I do think it is important to understand it so you get the best vape you can.