When a smartphone experiences difficulty charging after a physical impact such as being dropped, the most likely cause is damage to the physically damaged port. Ports can become bent or broken from impact, which can prevent the charging cable from making a proper connection. Alternatives like 'swollen battery' and 'overheating' may cause charging problems, but they are less likely to result directly from physical impact. Similarly, 'digitizer issues' could result from a drop, but they would not affect the device's ability to charge.