A phasing effect just with tracker-codes.
Basic material for this is are stereo-samples, split into 2 mono-files for L and R, used in diff. chans on the same row, set in the correct panorama, to reproduce the original stereo output. If so, an example :
Censor93_3.xm (http://www.samshuijzen.nl/sam/plainmods/censor93_3.zip)
Check the codes for 'start delay' and 'fine portamento up/down' in this case.