How to keep dirt out of the USB charging part on an iPhone?

I keep a silicone plug in the USB-C port and use wireless charging almost exclusively. Avoids a lot of headaches.

There are a number of products out there on Amazon that consist of a USB-C 'plug' that you put in the phone and has a magnetic attachment for a charging cable. I've never used one of those, but they look interesting. Some of them claim to carry data as well as charging the phone.

There's many cases with port covers out there to keep out dirt.

I use an Otterbox case with the rubber gasket cover. Its worked fine for me.

click here ➜ Otterbox Commuter Series Case - Amazon.com

You can get a charging port plug and take it out when you want to charge and put it back when not. And if you do decide to charge wirelessly you’ll never have to take it out and accumulate dirt and others stuff.

Yeah just look for a cover that has one of those little rubber flap thingys. They usually seal the port right off. I have one and no charging issues so far. Except when you make it a habit to fidget with the flap it’ll eventually fall off so try not to do that.

An internet search for "usb-c port cover" and "usb-c dust plug" turned up a number of possibilities. I haven't used any of them but I've never had a problem with the port.