bluetooth contectivity

Check the documentation for the JBL to find out how to put it into discovery/pairing mode. That should have been explained in there. The only way for the iPhone to "see" a device is for it to be in that mode. Generally, it needs to be powered on, and then it may need to have the power button held down for a moment. Most have a blinking light as well. This is just a guess for that device.

See this for help in connecting Bluetooth devices. Pair a third-party Bluetooth accessory with your iPhone, iPad, or iPod touch - Apple Support

If the iPhone will not connect to any Bluetooth devices and you believe it to be a hardware issue, then you need to make a Genius Bar appointment at the nearest Apple Store and have the device examined by Apple. They will explain your options. I suggest bringing the Flip with you as well.

It sounds like you have had the device connected to an iPhone before. I would check the Flip documentation as I said. You may have to reset it to have it connect to another device. Many speaker systems are not designed to retain information for more than one device, and have to be reset to connect to a new one. You can also contact JBL Support or check their website for additional support options.

See if this helps you --> https://tomstek.us/jbl-flip-4-pairing/