Ok, so let's say you have 0º, 40º, 80º, 120º, 160º and 179º. In this case you have 6 positions, that can be easily named {0,1,2,3,4,5}, or , for a direct correspondence to the info you´re receiving from the Bluetooth {48,49,50,51,52,53}. You can include in you sketch a switch-case condition that moves the servo to the nth position, whatever are the ones that fits your key.
PS: I´m obviously seeking the easiest/laziest solution 
to avoid implementing a more complex system to receive and parse a group of numbers in ASCII format. In any case, you might like to take a look in Serial Input Basics. It can be useful in the future.