There are a few reasons why you might not be able to hear your phone in your car. One possibility is that the volume on your phone is turned down too low. Another possibility is that there's something wrong with the audio connection between your phone and your car. If you're using an aux cable, for example, it could be loose or damaged.
If you're sure the volume on your phone is turned up all the way, and you're still not having any luck hearing it in your car, there are a few other things you can try. First, make sure that the source of the problem isn't with your car's audio system by playing some other type of audio through it (like a song from a CD or streaming service). If you can hear that just fine, then the issue is likely with your phone.
One thing you can try is restarting your phone, which can sometimes fix minor software issues that might be causing problems with the audio output. You could also try connecting your phone to another type of audio device (like a speaker or set of headphones) to see if you can hear it through that. If neither of those solutions works, then there's probably a more serious issue with your phone's hardware or software that will need to be addressed by a professional.