Arduino/phone jetski speedometer

Hey, I want to make a GPS speedometer for a jet ski. My wish is to use my iPhone for GPS. It would be connected over Bluetooth with some app, to an Arduino, which would be connected to a display. I am having trouble finding a good option to do this. I tried the blynk app, which I was able to connect to the Arduino, but getting speed tracking to work, was hard. I did get some sort of speed tracking to work with blynk but it is a number that doesn’t match any units (metric or miles) that I could figure out. Any ideas are appreciated!

someone already has GPS speedometer app https://apps.apple.com/us/app/gps-speedometer-and-odometer/id1448024273

Well, I want the app on my phone to send the speed data over Bluetooth to an Arduino.

Well, I want the app on my phone to send the speed data over Bluetooth to an Arduino.

Does the phone app work by itself? I've never written a phone app but it seems like you could measure and display the speed on the phone first. Then when that's working you can send the speed to the Arduino (in whatever units you wish).