I just don't understand how can I read data from a phone and guess it's baud rate.
You are not reading data from a phone. You are reading data from a bluetooth device. You do NOT need to guess the baud rate that the device communicates at. That is documented on the manufacturer's web site.
for instance, I can set my baud rate on the Arduino to 9600 which is pretty fine and the phone will auto tune to that baud rate).
What the phone does is not important. What the bluetooth device does is.
I'm working on a big project that I need to present in the next couple of weeks
So, you have a very complicated project, with lots of new stuff you've never used before, and it's taking longer than you guessed to get it all working. That bit about guessing is the problem. You should be tackling each piece of hardware with its own dedicated sketch, and no other hardware in the mix. Then, you'll understand, in the end, how to get it all to play together, and you'd have some experience to estimate how long the project will take. I can't get all worked up about you waiting too long to get started.