Q: Phone app connecting to call, counter ticks but no audio on both sides

Hello there repping!

Thanks for reaching out to the Apple Support Communities! It sounds like you are having an issue with hearing and being heard through your phone calls. I know how important it is to be sure phone calls are working properly at all times! Restarting is a great step to try and since you've done that and had a little bit of resolution, it might be best to see if there might be a software issue causing this. The best way to do that is to try out some steps from some articles. 

1. Be sure you have an up to date version of iTunes on your computer by checking out this article here: Get the latest version of iTunes. Also, make sure your computer is running the latest software update on it. 
2. Backup your device by following the steps in this article: How to back up your iPhone, iPad, and iPod touch. 
3. Follow the steps in this article: Use iTunes on your Mac or PC to restore your iPhone, iPad, or iPod to factory settings.
4. Set the phone up as new and make a test phone call to see if the issue is still going on, then follow the steps in this article to restore the backup: Restore your iPhone, iPad, or iPod touch from a backup.

Cheers!