The most important thing to connect both speakers to your phone is connecting only one speaker through bluetooth.
When a jbl flip4 connected through bluetooth, the power button turns blue. So your 1st flip4 should be blue light on power button and another is white.
Try this way;
1. Turn on both speakers and confirm only one connected to the phone.
2. Open JBL connect app on your phone.
3. Turn on JBL connect+ button on both speakers.
4. Wait a moment and the JBL connect app will show the two speakers are connected to your phone. You can toggle party/stereo mode on the app.