According to FP’s new Impact Report (PDF), the bottom module is the part that failed most often in 2017.
I must say that I’ve seen many USB ports of the Fairphone 1 fail and this means that the whole motherboard has to be replaced as resoldering is not reliable. A replaceable bottom module seems to be the better strategy in this regard. Keep in mind that the USB port receives the most stress in a phone because you attach the charging cable every day. (A magnetic cable helps in this regard: 🇬🇧 🇩🇪 Magnetic USB cable recommended to avoid socket probs)