when I plug in my charger there's like a 3 seconds delay before my iphone recognizes it and vibrates and charging symbol appears

If the power source is a USB-C/PD it can charge at several different voltages and currents. It and the phone have “discussion” about what the phone actually wants. This takes a second or two normally, 3 seconds is a little high, but how carefully have you timed it?

Bad cable, bad adapter, line in the charging port, a malfunction in the charging port. Probably other things.

Is your phone charging properly? If so, I probably wouldn't worry too much about it.