Start with the cable and charger, because it's free to check. Try a different cable and a different wall adapter that you know work on another device. If the phone charges, you're done. If it charges only when the cable is held at an angle, keep reading.
Next is the port. Pocket lint compacts into the bottom of a charging port over months until the plug can't seat fully. We clean ports at the shop in minutes, and it fixes a surprising share of 'won't charge' complaints. If the port is physically worn or the pins are damaged, the port itself gets replaced, which is a same-day repair on most phones.
The third possibility is the board. If the phone doesn't respond to any cable, gets hot at the bottom while charging, or died after liquid exposure, the fault is usually a charging IC, a shorted line or a damaged pad on the motherboard. That's micro soldering work, done under a microscope, and it's the repair most shops either send away or decline. We do it at our bench in Sarasota.
You don't need to guess which one it is. Bring the phone in, the diagnostic is free, and we'll tell you exactly where the fault is and what it costs to fix before we touch it.