Hey Phixphn,
Thank you for using Apple Support Communities!
We understand that you're having issues with Siri on your iPhone and we'd like to help you.
To start, go to Settings > Siri & Search > Voice Feedback and make sure this is set to Always.
Next, open the Control Center and expand the audio card. This is located in the upper right corner. Make sure that your device isn’t connected to any other audio sources. If you see something other than iPhone listed as the audio source, change it and test Siri again. You can see steps for this here: Access and customize Control Center on your iPhone and iPod touch
While making a Siri request, try turning up the volume while Siri is responding as mentioned here: If Siri or "Hey Siri" isn't working
We also recommend to try setting a different voice for Siri, then testing it out and putting the voice back to your preferred choice. You can do that by going to Settings > Siri & Search > Siri Voice. If American (Female) is selected, try selecting the Male voice to test, then change it back and test again.
Cheers!