How do I know my pulse rate if I want to monitor my BP with my phone device.

Can easily count HR. Most devices or instruments that measure BP will assess a heart rate, but you can also easily count the pulse yourself. Just find your pulse (typically at your wrist or at your neck) and count the number of beats in a minute, or you can count for part of a minute and multiply (i.e., count the number of beats in 10 seconds and multiply by 6 to get a heart rate).