Hi Carla,
Do you mean a phase of a particular job, or a phase code that could be applied to any job?
At the current time, you cannot make phases inactive nor hide them from grids. The best you can do for phase codes is to delete them (if no jobs have estimates defined with it), or change the description to something like 'Do not use'. Typcially, phase codes are generic in nature and get applied to various job estimates.
If you mean a phase of a particular job, there is no way to prevent creating cost or billing batches against a phase. Though that sounds like an interesting idea for a future release.
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Regards,
Softrak Tech Support