It's either a (bad) solder joint to the phone jack (likely), or the spring-loaded operation of the phone jack itself.
Either way I would just take it to your tech. It's a one-hour job or less (to remove the I/O board, fix jack, and reinstall I/O board).
It's a standard phone jack, your tech will probably know the part already, or you can ask Arturia for the part # they use and you can cross reference.