We 'phase' our projects more often than not, but you do need a handle on the whole building to do so. Most of the time advantage come from the permitting process: it takes us 8-10 weeks to get a full permit, but only two weeks to get a foundation permit. And TIs can be added later.
Our process is: model as much of the project as needed in order to engineer the foundations and provide whatever else the permitting authority may require (in our case, structural floors plans and elevations as well as foundation details). When this task is completed and printed, save that model under a new name (PROJ-FNDN) and archive it.
Then return to the original model and finish the full permit plan set.
For TIs, reference the full permit model into a new model and complete the TI. There are various approaches to multiple TIs. We generally keep them separate, which means that we never have a single model of the entire project, but we seldom need one. If you want the entire project in one file, I would reference each TI into a shell model (do not include nested modules and be careful of 2d annotation, which will add confusion).
James C Lewis
AC 24 (Full)
Mac Pro (Late 2013) OS 10.13.5