Hi @Werner_Beck; this is a great question!
Piggy backing off @Brian_Titus & @Mark_Nattress suggested, tags are a great way to keep track of phases, in lieu of custom fields; a feature available for premium Asana members. A brief discussion on the efficacy of & difference between tags vs custom fields is discussed here..
Sections can be a great visual cue as well, which are able to be created by adding a full colon after the name of a Task. For folks who are more of the visual learners, our Boards Project view is a great way to create Projects that make it easy to identify where certain Tasks are at, by associating columns with periods of time (months/quarters etc).
Projects also have a Progress tab that allows you a basic chart of the Project’s “health”, like what percentage of Tasks & Subtasks have been completed. You can also use Project status updates to inform all Project members of the your report on Project achievement, your customized alerts of milestones achieved or those that hovering close on the horizon.
Additionally, if you load your Project into your Dashboard, our Google Sheets reporting integration will allow you to dig a bit deeper. Using the live data from the Project you’ve loaded into your Dashboard, you’ll be able to get a close up lens on how far you & your Team have come & how much farther you have to go.
Hope this provides an idea of various ways you’re able to use features in Asana to capture & represent phases of your Team’s work, whether you’re a free or premium Asana user!
Let me know if you have any questions!
PS: I do want to note a brief caveat on Subtasks. They are absolutely great to add necessary details to a Task however I would warn against delving too deep with more than one layer of Subtasks. Asana allows you to delve up to 5 tiers of subtasks deep, which can make them quite easy to miss & lose track of. They will also make your Projects slower to run if one Task has over 50 subtasks (for example) nested in just one Task. Hope this helps!