What's the port on the lower left edge of my iPhone 14?

Alan,

That port can accommodate a physical nano-SIM card which can be used (if you want) in combination with any eSIMs provided by your cellular carrier, according to this configuration:--> Using Dual SIM with an eSIM

Contact your cellular carrier about that.

To open the SIM card tray/holder, see the following instructions:--> Remove or switch the SIM card in your iPhone.

Regards

Giulio

Extracted from this page:--> iPhone 14 - Technical Specifications

External Buttons and Connectors

1. Front camera
2. Side button
3. Lightning connector
4. SIM tray (available on models purchased outside the U.S.)
5. Volume buttons
6. Ring/Silent switch
7. Rear cameras
8. Flash

It’s the phone's microphone.

I misinterpreted your question to mean the left side of the bottom. As Giulio’s image shows you must be seeing the SIM slot.