To clean iPhone speaker holes turn the iPhone off and remove the case if you have one.
Then take a small, soft bristled brush, like a new dry toothbrush and gently brush the speaker grills.
You can also use a cotton swab to brush the iPhone speaker holes to clean it or use a gentle burst of some can compressed air.
A sticky putty like AirSquares can also be used to lift any stubborn dirt or debris out of the iPhone speaker holes or use a wooden toothpick to gently and carefully dislodge any visible debris and angle the iPhone speaker holes so taht it will fall out without pushing it in further.
You can also clean a USB-C port by using a gentle burst of some compressed air from a can of air, which can blow out any loose debris.
You can also use a toothpick or anti static nylon brush to carefully dislodge any remaining lint or dirt.
Just be careful to avoid the contacts inside the port which are delicate and easy to damage.
You can also use a cotton swab dipped in 70 percent isopropyl alcohol and swipe it gently inside the USB-C port and allow it to air dry completely before you use it.
You can also use the end of a plastic dental flosser to clean the inside of a USB-C port as it's thinner than a wood toothpick and also less likely to break and leave splinters in the port.
I always at least once weekly will use a can of compressed air and spray out the inside of the USB C Ports as well as USB and HDMI ports on my computer and charging ports and headphone ports on my phone to keep them clean and free of any dirt or debris.