I bricked my wireless CarPlay dongle half year ago. I love that dongle but I wanted to try using my old phone instead of getting a new dongle. I finally bought a new iPhone last week so I had spent time to set my old phone up and leave it connected all the time in my car. I am pretty happy with this solution. The only problem is I can’t make or receive wireless phone calls unless I unplug my CarPlay phone because it doesn’t allow HF Bluetooth phone call if CarPlay is connected. That’s not a big deal for me since I usually don’t make phone calls when I’m driving. I set up my old phone to join my personal hotspot automatically so it always has internet connection. I set up automation to enter low power mode when CarPlay is off. The battery can last pretty long.
If you log in to iCloud on the old iPhone, you should be able to set answer calls on other iPhones and the old would should ring. That said, I don't understand why you are using an old iPhone. If the new one is using hotspot to supply data to the old one, the battery will be drained pretty quickly. I've actually been looking at a magnetic lighting connector instead to avoid the plug in all the time. Ideally, if we could use wireless carplay I would get a magsafe charger stand or puck.
In iCloud settings, I can only choose to receive iMessage or FaceTime, not phone calls or text messages. Thanks for pointing out that setting. It’s not a big deal. If I really want to dial through my screen, I could simply unplug my old phone. My new phone will have HF Bluetooth enabled automatically. I use my old phone because I don’t want to take my phone out of my pocket for short trips. The wireless dongle I bricked before is still a decent solution. It’s a bit slow on startup but worked very well.
