Currently, IDQ does not have the FTP/SFTP connection type directly. If you are using workflow in IDQ then, you can use a command task to run a script that SFTP the source file to the IDQ server machine. Then, use the file in the mapping task later in the workflow.
An additional option might be to use an ODBC bridge between Linux and Windows machines via SequeLink. This option is usually taken into account when you need to read an excel file stored on a Windows machine from an Informatica server running on Linux. Although, it might also work on your scenario.