Hi HelpingMyDad29,
If you'd like Siri to respond, these steps might help.
Have you had the chance to try a restart? We know this may seem like a simple step, but it resolves issues both big and small.
How to restart your iPhone SE (2nd or 3rd generation), 8, 7, or 6
1. Press and hold the side button until the power-off slider appears.
2. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
3. To turn your device back on, press and hold the side button until you see the Apple logo.
The information above is from Restart your iPhone.
If the issue continues, then you'll want to check out the microphones on your Dad's iPhone. Follow the steps below from If the microphones on your iPhone aren't working.
1. Remove any screen protectors, films, or cases from your iPhone.
2. Clear any debris from the openings of your iPhone.
1. Open the Voice Memos app.
2. Tap the Record button
, speak at the bottom of your phone, then stop the recording.
3. When you play back the memo, you should hear your voice clearly.
4. If you don't hear your voice clearly, contact Apple Support.
Since Siri uses the same microphone as in FaceTime or Voice Memos, this is a good test to see if it could possibly be an issue with the microphone.
We hope that helps with your question and take care!