Is there an ECG App for iPhone?

Assuming you are over 22:

”Install and set up the ECG app

The ECG app  is installed during the ECG app setup in the Health app. Follow these steps to set up the ECG app:

1. Open the Health app on your iPhone. 
2. Follow the onscreen steps. If you don't see a prompt to set up, tap the Browse tab, then tap Heart > Electrocardiograms (ECG) > Set Up ECG App. 
3. After you complete set up, open the ECG app  to take an ECG.

If you still don’t see the app on your Apple Watch, open the Watch App on your iPhone and tap Heart. In the ECG section, tap Install to install the ECG app.”

What country are you in and what country are the Watch and phone from?

Take an ECG with the ECG app on Apple Watch - Apple Support

watchOS - Feature Availability - Apple

Because the ECG app is only on the Apple Watch.