I would recommend placing a phone call from your Oneplus 6 to a landline or to a second cell phone you have an hand. Generally most phones use the upper microphone to aid in noise cancellation. They also use the upper microphone as the primary input when you have the device in ‘speakerphone’ mode.
Test your microphone like this: (Phone A = Oneplus 6, Phone B = second device.)
- Call yourself.
- After answering the call, place a finger over the microphone hole on Phone B. This will eliminate the feedback produced by holding two phones so close together during a call. Continue to cover this microphone for the duration of the test.
- Hold the speaker of Phone B up to your ear. Hold the bottom edge of Phone A (OnePlus 6) up to your mouth and speak in a normal tone. You have just tested your primary microphone.
- Press the ‘speakerphone’ button on Phone A. Hold the top edge of Phone A up to your mouth and speak in a normal tone. You have just tested you secondary microphone.
If both mics sound normal then you have no damage to the microphone components. Honestly I think all you did was puncture a moisture barrier or a dust barrier. The vast majority of phones I work on which have a mic hole at the top of the device near the SIM tray hole take user error into account during design. Manufacturers assume the customer may stick the pin into the mic hole. Therefore, the mic is usually NOT mounted directly under the hole. Instead there is a rubber channel that take s a 90 degree turn. So you end up either stabbing the rubber cap (harmless) or stabbing an ingress protector of some kind, which just makes the phone less water-resistant.