Each time a Phantom launches, it needs to load the input spreadsheet.
Some input files are a few hundred lines, but others are way bigger. It takes about 1 second to load 1000 lines. So, if your file is under 10k or 20k lines, that's fine. However, some of our users are loading files with 2m+ lines at each launch. This means 30+ minutes of loading time per launch!
If you have this much data to process, we'd recommend dividing it up and using smaller input files to save your execution time - try dividing big files into sheets of 30k lines.