No, i is changing so the filename is changing. Try to split it up
for k = 1 : 10
% code to RUN PROGRAM and change phi...
% Now save this phi in a new file.
filename = sprintf('datafile_%02d.mat', k);
message = sprintf('About to save phi into new file %s.', filename);
uiwait(helpdlg(message));
save(filename, 'phi');
end
Now see if the filenames are all the same or different.
