Unfortunately there’s a number of different possibilities and things to check.
Make sure of the cable and PC USB port by connecting the PC to some other data source such as another phone or an external drive.
Have you in the past successfully connected the FP6 to another USB data source or target, such as wired headphones through a Digital to Analogue Converter (DAC), or a USB hub?
When charging the phone do you successfully use fast charging?
Make sure the FP6 USB port is clean. The smaller and more complex these connectors get, the more sensitive they are to grime and grease. To clean the port of fluff and lint use a small cleaning tool attached to a vacuum cleaner, or a can of compressed air, possibly also a fine plastic point such as a toothpick if necessary. Be careful, the central microboard is fragile.
Has the phone ever been opened, for example to replace a part? There may be a problem with the USB port module’s internal connector.